I think that is highly unusual. I have claimed expenses from a variety of employers and clients and never experienced this.I think a lot of assumptions are made regarding travel expenses which have no basis in fact.
I often travel to a facility which means I need to go from my home village, in Midlothian, to Didcot Parkway. They, not my employer, pay for travel. The cost of a Super-Off peak single is now a tad over £115 and can sometimes, but not always, be brought down by split ticketing. However, last year the facility decided to apply a limit on travel expense claims as a way of saving money, with four different claim limits depending on distance (£50, £100, £150 and £200. Anywhere which is Newcastle and beyond can now claim no more than £200. Thus if I only buy Super-Off peak tickets I will be £30 out of pocket, and the conditions of claiming make it clear one cannot claim from another source (which would be fraud) so my employer cannot make up the shortfall.
Attempts to protest this, armed with evidence, fell on deaf ears. Of course, those travelling from London are OK as an off peak return is £12 lower than the first claim limit![]()
However it's not completely unheard of either; I remember at least one other person describing a similar principle, but it's certainly not the norm.