The choice is yours - there's no official guidance on this
The Department for Education doesn't have specific rules on this. That means whether staff can pop a cork or two is at the discretion of the headteacher and the governing board.
Check with your local authority (LA) first if you're a maintained school because it may have its own rules.
Be sensitive to your staff’s needs
This is especially important if the event is mandatory or there’s a clear expectation that staff will attend – for example, a goodbye party for a long-serving school leader. You should always have non-alcoholic options available as well. If staff are uncomfortable being around alcohol for any reason, be willing to make adjustments.
If pupils are going to be at the same event, you’ll need to set out clear rules for staff on whether they can