Well first thing, you cannot do the ATPL theory on your own, the caa form needs to be signed off by a well known flight school before the caa will let you in for the exams. So basically you'll have to do a "distance learning course" and do 2 weeks ground school or the amount of ground school hours the caa regulates. You can do this in schools such as BGS or GFS in bournemouth.
Well everyone has different opinions if you should do this conversion, but I would say no, as firstly in the uk to work your going to need to have a work permit or somthing that will allow you to work in the uk. Secondly theres pilots in the uk or europe with alot of experience and no jobs currently, even after this reccession those pilots will probably be going back into the pool first... so basically my answer is "no"...