We have an old roll top cast iron bath which has taps which come
through the sides. I believe they are called "globe taps" (http://
http://www.salvo.co.uk/images/userim...67/26988_1.jpg is a picture I
found).

I'm no plumber (!), but I reckon a dripping tap ought to be within my
capabilities. I expect the issue to be a failed washer, so I will
need to turn off the water supply, remove the top, replace the washer
etc.

Things I need advice on:-
- its the hot water tap, and we have a combi boiler. Do I turn off a)
the boiler b) the cold water feed c) both the boiler and the cold
water feed? Which combination is best for the boiler, best for me!!
- what size washer is likely to be required in one of these taps? I
would like to have the most likely culprit available to hand, so if
its going to be something non-standard it would be good to know in
advance! I believe most bath taps use 3/4" washers?
- any likely pitfalls I'm going to fall into with this type of tap? I
would much rather not have them at all, but SWMBO likes them. I know
that they are not an approved type of tap these days (something to do
with water from the bath being able to get into the cold water
supply?) but I presume someone has some experience of them?

Thanks in advance for any help!

Matt