The BGS question bank is pretty much as close to the real thing as you can get, however, do be aware the CAA are totally within their rights to reject some or all of the JAA questions and replace them with their own totally new ones.
With my first set of ATPLs, the large majority were on Bristol - but for some questions involving calculations, BGS won't be too much help (i.e. M&B, GNav)
HTH