A £1200 focus is going to be (as said) bottom of the barrel stuff.
prices have risen on focus quite a lot the last 6 months due to supply and demand. a year ago you were spoilt for choice on a focus, not now days.

Id say yes go for a mk3 golf.

Half decent ones are going for about £1k, so 1200 should find you a half decent one.

dont expect a minter for that money, but you will get a good reliable car for that price.

Check for rust on rear arches and lower rear 1/4 sills.

Also mk3/4 are prone to electrical problems, but only cosmetic, usually you will fint the blower and heating vent lights dont work, sue to a shit built in bulb you cant replace. and also they seem to over charge on the alternator a little, which is why you always see mk3/4 golf with a side light bulb or brake light out.

As long as it has a good service history, you cant normally go wrong with a vw.

You may if your lucky even find a mk4 shape BORA TDI for that money. 1.9tdi 130bhp 50+mpg and just as quick as the mk3 gti.

Im on my 3rd golf now (which is my 6th VW!!!) cant go wrong with them IMHO.

If you want some decent links to help you search just ask, as im using about 6 Vw forums at the mo to sell my mk2 VR6.