Looks like I may have to fly back to the Uk soon due to parent's illness. Have only just got retirement visa what is the best way to get the reentry permit. I've heard they are available at the airport but takes time.

I would get at an immigration office rather than last minute at airport where you might be pressed for time (and if you forgot photo out of luck).

Thanks. Is the photo all that I need. Presumably the reentry permit runs until the expiration of the visa...right?

The re entry permit will be valid until the permitted to stay until stamp in your passport. On return you enter the re-entry permit number/information where you would normally enter visa information on arrival card.

There may be a photo copy of passport required at some places. Bangkok offers semi on-line service by using the featured service information on this web site (you send form one day and present yourself/photo/fee next day). The fee for single entry is 1,000 baht and for multi entry is 3,800 baht.