If I book a return ticket through a local agent in the UK, can I pay in cash?

Actually, there are air ticket agents everywhere.

However, everyone likes to go to London, because the return ticket there will be relatively cheaper.

As for the payment method you mentioned.

Of course, no problem. Cash payment is also acceptable. There is no need to worry about this.

Relatively speaking, at this time, I don't know if there is a Chinatown in Durham, but what I do know is that,

It seems to be close to Newcastle, where you may find a ticket agent like Omega.