These are on eBay.co.uk by a US seller. Are they legal for UK use?

I don't think so. FRS/GMRS specs are US-only IIRC. Look at this UK resller page.

Most people who have them in the US use them illegally by not geting the GMRS license from the FCC. I actually bought the license though. I think it was $75 and is good for 8 years or so.

This page shows that some of the frequencies are used by UK ships. A quick google search for UK radio allacation should return the radio map which indicates which bands are subject to which radio licenses (and which do not require the use of a license).

Try screwfix.com product 75189 for inexpensive site communications up to 3km. Alternatively, Motorola do a product that works upto about 10 miles but requires a license and an allocated callsign - I can't remember the name of the system, you'll have to do a little light research. There is also private business radio.