diff --git a/app/controllers/session.js b/app/controllers/session.js
index 576084da0..7671dc41d 100644
--- a/app/controllers/session.js
+++ b/app/controllers/session.js
@@ -745,8 +745,14 @@ export const sessionController = {
       }
     }
 
+    const sessionWithFullContext = new Session(session, data)
+    if (session.type === SessionType.Clinic) {
+      response.locals.appointmentsToCancel =
+        sessionWithFullContext.appointmentsToCancel
+    }
+
     // Give access to the data needed for the summaryRows
-    response.locals.session = new Session(session, data)
+    response.locals.session = sessionWithFullContext
 
     // Show back link to session page
     response.locals.back = session.uri
diff --git a/app/locales/en.js b/app/locales/en.js
index 009f37d25..2b3029f06 100644
--- a/app/locales/en.js
+++ b/app/locales/en.js
@@ -2546,7 +2546,14 @@ export const en = {
     },
     edit: {
       title: 'Edit session',
-      success: '{{session.name}} updated'
+      success: '{{session.name}} updated',
+      appointments: {
+        cancellation: {
+          title: 'Appointments will be cancelled',
+          description:
+            '{count, plural, one {Changes made to this session will result in the cancellation of **1 appointment**.\n\nA notification will be sent to the parent or guardian of the affected child, inviting them to book a new appointment.} other {Changes made to this session will result in the cancellation of **{count} appointments**.\n\nNotifications will be sent to the parents or guardians of affected children, inviting them to book a new appointment.}}'
+        }
+      }
     },
     cancel: {
       bookings: {
diff --git a/app/models/clinic-booking.js b/app/models/clinic-booking.js
index ef46f7d2c..0716c00af 100644
--- a/app/models/clinic-booking.js
+++ b/app/models/clinic-booking.js
@@ -2,6 +2,7 @@ import { fakerEN_GB as faker } from '@faker-js/faker'
 import _ from 'lodash'
 
 import { ClinicAppointment, Contact } from '../models.js'
+import { today } from '../utils/date.js'
 import { formatCode, stringToArray, stringToBoolean } from '../utils/string.js'
 
 /**
@@ -10,6 +11,7 @@ import { formatCode, stringToArray, stringToBoolean } from '../utils/string.js'
  * @param {object} [context] - Context
  * @property {object} [context] - Context
  * @property {string} [uuid] - Clinic booking UUID
+ * @property {Date} [createdAt] - Created date
  * @property {string} [bookingReference] - Booking reference number
  * @property {Array<string>} [invited_programme_ids] - IDs of programmes for which child was invited
  * @property {Contact} [contact] - Contact details for the booking; see appointments for parental relationship details
@@ -19,6 +21,8 @@ export class ClinicBooking {
   constructor(options, context) {
     this.context = context
     this.uuid = options?.uuid || faker.string.uuid()
+    this.createdAt = options?.createdAt ? new Date(options.createdAt) : today()
+
     this.bookingReference =
       options?.bookingReference || ClinicBooking.generateReference()
     this.invited_programme_ids = options?.invited_programme_ids
diff --git a/app/models/clinic-vaccination-period.js b/app/models/clinic-vaccination-period.js
index 44171edcb..97fac266e 100644
--- a/app/models/clinic-vaccination-period.js
+++ b/app/models/clinic-vaccination-period.js
@@ -12,9 +12,7 @@ import {
  * @param {object} options - property values
  * @property {string} [uuid] - Vaccination period UUID
  * @property {Date} [startAt] - Start time of first appointment slot
- * @property {Date} [startAt_] - Start time of first appointment slot, from dateInput - see getter/setter
  * @property {Date} [endAt] - End time of final appointment slot
- * @property {Date} [endAt_] - End time of final appointment slot, from dateInput - see getter/setter
  * @property {number} [vaccinatorCount] - The number of staff vaccinating in parallel during this period
  */
 export class ClinicVaccinationPeriod {
@@ -22,9 +20,7 @@ export class ClinicVaccinationPeriod {
     this.uuid = options?.uuid || faker.string.uuid()
 
     this.startAt = options?.startAt && new Date(options.startAt)
-    this.startAt_ = options?.startAt_
     this.endAt = options?.endAt && new Date(options.endAt)
-    this.endAt_ = options?.endAt_
 
     this.vaccinatorCount = options?.vaccinatorCount
   }
@@ -92,6 +88,26 @@ export class ClinicVaccinationPeriod {
     }
   }
 
+  /**
+   * Does the given appointment start time fall within this period?
+   *
+   * @param {Date} appointmentTime - the start time of appointment
+   * @param {number} appointmentLengthInMinutes - the length of slots in minutes
+   * @returns {boolean} - true if the slot falls within this period, or false otherwise
+   */
+  includesAppointmentTime(appointmentTime, appointmentLengthInMinutes) {
+    const firstSlotTime = this.startAt.getTime()
+    const lastSlotTime = addMinutes(
+      this.endAt,
+      -appointmentLengthInMinutes
+    ).getTime()
+
+    return (
+      appointmentTime.getTime() >= firstSlotTime &&
+      appointmentTime.getTime() <= lastSlotTime
+    )
+  }
+
   /**
    * Get formatted values
    *
diff --git a/app/models/session.js b/app/models/session.js
index e6bf82ee2..0a6c9030c 100644
--- a/app/models/session.js
+++ b/app/models/session.js
@@ -620,6 +620,38 @@ export class Session {
     return appointments.filter(({ patient_uuid }) => !patient_uuid)
   }
 
+  /**
+   * Get a list of the appointments already made but for which we don't have capacity
+   *
+   * @returns {Array<ClinicAppointment>} - the appointments we'll need to cancel
+   */
+  get appointmentsToCancel() {
+    const allAppointmentsByTime = _.groupBy(this.appointments, (appointment) =>
+      appointment.startAt.getTime()
+    )
+
+    const appointmentsWithoutVaccinators = []
+    Object.entries(allAppointmentsByTime).forEach(([key, appointments]) => {
+      const startAt = new Date()
+      startAt.setTime(Number(key))
+      const vaccinationPeriod = this.vaccinationPeriods.find((period) =>
+        period.includesAppointmentTime(startAt, this.appointmentLength)
+      )
+      if (!vaccinationPeriod) {
+        // No longer part of a vaccination period, so cancel all appointments at this time
+        appointmentsWithoutVaccinators.push(...appointments)
+      } else if (vaccinationPeriod.vaccinatorCount < appointments.length) {
+        // Not enough vaccinators at this time, so those who booked first get to keep their appointments
+        appointments = _.sortBy(appointments, 'booking.createdAt')
+        appointmentsWithoutVaccinators.push(
+          ...appointments.slice(vaccinationPeriod.vaccinatorCount)
+        )
+      }
+    })
+
+    return appointmentsWithoutVaccinators
+  }
+
   /**
    * Get school
    *
diff --git a/app/views/session/edit.njk b/app/views/session/edit.njk
index 18850231d..bb74e8f42 100644
--- a/app/views/session/edit.njk
+++ b/app/views/session/edit.njk
@@ -86,5 +86,14 @@
         totalAppointments: {}
       })
     }) }}
+
+    {% if appointmentsToCancel.length > 0 %}
+      {% set detailsHtml = __mf("session.edit.appointments.cancellation.description", { count: appointmentsToCancel.length }) | nhsukMarkdown %}
+
+      {{ warningCallout({
+        heading: __("session.edit.appointments.cancellation.title"),
+        html: detailsHtml
+      }) }}
+    {% endif %}
   {% endif %}
 {% endblock %}