Ghengis, having done it myself, I think that the few hours of training that you need to convert to group A nppl from microlight are the easiest training hours I ever did. I did mine in minimum hours and I'm sure many others could too.
There is a caveat though: I had a few years and over a hundred hours on 3 axis microlights. I think it still would have been achievable with 6 months and 20 hours of 3 axis microlighting though.
To the OP: You can now hire microlights and thats what I would plan to do to build hours and experience before doing the group A conversion. Typically you have to pay a monthly fee of around £45-60 and then hourly its about £45-55.
This is a very cheap way to build hours and provided you stretch yourself by doing lots of different trips then you'll quickly be in a position to do the conversion in minimum hours.