Highly unadvisable.
I tried to do my British IR part time with Stapleford Flying Club while living in London last year (I already had 750 TT, a New Zealand IR and about 100 hours IFR time logged in that country). It took me 5 months part time, most of that was wasted effort, I simply couldn't get myself up to the standard required by flying on a part time basis. In the end my instructor told me to stop wasting my money and not come back until I had quit my job and could devote full time effort to it. I got through it first time in the end after a couple of weeks of intensive training, but I reckon I'd probably still be trying to pass it now if I had kept on trying to do it on a weekend basis.
It may be do-able part time by better mortals than myself but for anyone it would be a MASSIVE additional effort. The UK/JAR IR is without a doubt the hardest flight test in the world, less than half of the applicants get through it first time.