Endorsement of a UK cheque, either "in blank" or to a named third party, was legal at one time, though the practise was dying out in the 70s & 80s when I was involved as a bank counter clerk (US teller) and was never really liked by bankers.

Around the 90s legal status was given to the special crossing "Account Payee" which was previously little used and could be legally ignored by a collecting banker, though at his own risk in the event of non-payment of the cheque. The crossing suddenly gained great popularity, and is now just about universal. The effect of the crossing is to make the cheque non-transferable, so your friends are unlikely to be able to help you.

I am assuming here that your cheque has on its face 2 vertical or near vertical lines, with the words Account Payee close by. If this crossing is absent and your friends know their local bank staff well enough to avoid having to deal with a jobsworth (and believe me banks attract them like flies to roadkill) then they might be able to help.

Assuming you originally paid by card I would send the cheque back to the bus company and insist that they refund your card as originally instructed, telling them why, as they are unlikely to work it out alone. They do have the means to do this, it is a requirement of being a card merchant. It is even in their interests as they will get back the percentage they had to give the card company to accept your card in the first place, and will not have to pay the bank charge for issuing your cheque.

As a slight thread drift, does anyone know why US banks are so widely unwilling to deal with foreign cheques and currency? Such things are quite commonplace in UK banking, and both overseas visitors and such cases as this one must be becoming more frequent.