An employee who is a supervisor for a chain of supermarkets has to visit different outlets. Each outlet is a temporary workplace (see EIM32075), so she is entitled to a deduction for the full costs of travelling between her home and each outlet.
In addition she is invited to the Christmas parties at each
outlet. No deduction is due for the cost of her travel to attend
The outlets are temporary workplaces for those visits she has to make but they are not workplaces for those visits she chooses to make for non-work purposes, see EIM32180. The travel to attend Christmas parties is private travel.