I would appreciate details, please, of where I can buy 'frog mugs' -
preferably from a reputable source, online and in the UK.

Frog mugs have a ceramic frog sitting on the bottom of the inside of
the mug, ready to surprise unsuspecting drinkers. The one I saw,
bought several years ago at an unnamed place in London, had inscribed
on the side "Frog mug - a quaint reminder of 18th-century tavern
humour".

You can see an example of a frog mug at
http://www.studiopottery.com/pots/03082b.html.

I do not want to buy antique frog mugs, only new ones.

Hope somebody can help me solve all my Christmas present woes early!
Many thanks

This USA company has them:
http://www.dlgallerygifts.com/HandMadeCeramicArt.html

Here are two from a U.S. merchant:

http://www.frogstore.com/products/SD2607MG.asp

http://www.frogstore.com/products/SD1443SM.asp