HMRC Employment Manual paragrah 31835 says“The tests that apply to travel expense relate to the nature of the expense and not to the amount.” It goes on to say: “You should not refuse a deduction for first class rail travel, if that has been incurred, on the basis that the same journey could have been made more cheaply in standard class”. As long as the travel and hotel costs were incurred wholly and exclusive for your business the full cost is tax deductible.
The cost of providing the Christmas lunch for staff will be tax deductible.
The lunch can be tax free for the employees if it is in the form of an annual event or number of events to which all the staff are invited. However, you should try to limit the annual cost to £150 per head, counting all those who actually attend the event. If the costs exceed £150 per head (including VAT) your employees will be taxed on the total cost per head (not the excess above £150) as a benefit in kind.