Have just arrived for 42 days on a 60 day visa but have to return to UK urgently for 5 days. When I return I will be staying 29 days so I plan to just enter on a normal tourist visa. However the hotel is telling me I have to go to immigration office in Hua Hin and pay 1000 baht to do this.........?? Can anyone confirm if this is nevessary?

If you return by air, you will get a visa exempt entry of 30 days. (presuming you are a UK national and you already have the return flight back to the Uk for after your 29 days)

No need for a Re Entry Permit if you are returning for a stay of under 30 days and have an exit flight ticket.

No need. They're talking about a re-entry permit. If you just leave your existing 60 day visa (which isn't multiple entry anyway) will automatically cancel. When you return you don't need to bother applying in the UK for another tourist visa - since you're staying less than 30 days, just get a 30 day exempt stamp on arrival.