International travel expenses

[Lance]

Employee travel expenses aren’t cost of goods sold. Are you even selling goods, for starters? The cost of reimbursing employee travel costs is an administrative expense. It could come under staff costs or simply travel.

yep.

Travel costs are 'travel'....
Accomodation costs are accomodation.
The fact that the client will allow yourCO to bill them is just another invoice.

Some over-thinking is goin on here. The only factors of relevance are the 24 month rule, and whether it is wholly and exclsuivelt for business.
On the former, it's a temporary place of work...
On the latter, if the client is paying then HMRC are going to look no further.