Hi,to stop the dogs running out of the front door I need to be able to put a lock on the living room door,it needs to be lockable/unlockable from both sides,the door has just a handle with no lock at the moment,what do I need to buy?

Just put your handles upside down ,we had to do that with our dog when we where kids

Or a simple little brass bolt either side.

or fit a cheap child gate, that keeps my two dogs at bay.

chances are the door only has lever handles and a small mortice latch. To replace that with a sash lock would need a bit of joinery work to cut mortice out--not so easy on an interior door.
Cheapest option is the small brass bolts --around £2. You may need a "necked" one on one side of door and to drill a small hole in frame. The bolt keep on the other side can be a bit awkward to fit because of the architrave. The problem of a bolt on each side is that others can lock you in!

Or swap the existing door fixture for Union 64mm sash lock or similar to that shown below.

Cabin hook and eye on each side would work.Cheap and effective.

Thanks for all the suggestions,in the end I found that the bathroom door had a lockable handle,switched them over,works fine.