Checking Battery is holding charge

More information needed. Do you mean you want to check if something on the car is drawing current from the battery when everything is switched off?

if you want to test whether the battery is in good condition then take it to any car shop, they will have a tester. or an AA patrol.

do they have special testers? is a multimeter no good for checking this?

No, you need something like this

John was thinking very hard :

They have a special type of meter which applies a large load current and checks how much the voltage falls on load over a set period. They will usually carry out the test for free, on the off chance you may buy a new battery if it is demonstrated to be faulty. You cannot do that with an ordinary cheap multimeter, all you can do is check the static volts. It should read something better than 12.5v after standing for a while, but it is not absolute proof that it is OK, just an indication that it is retaining some sort of charge. When cranking, but not actually started it should be over 10.5v.

Although that normally tells you all you need to Know :-)