Line training is airline induction after you have your type rating.
You need CPL / ME-IR / MCC and a pass in the ATPL exams before you can even think about type ratings (and before anyone says anything, I know you can get a type rating endorsed on a PPL which is, of course, a pointless exercise unless you happen to own a very large aircraft).
Even once you get to this stage, there is NO chance of anyone employing someone with 250 hrs on any variety of B747. You might get somewhere with the Bombardier types but it is generally better to wait and see what type of aircraft your future employer is using. In most cases, they will have some sort of funding arrangement for obtaining the rating. The typical cost of a TR is usually about £25k once you include the base training.
The number for the CAA can be found on the medical section of their website. Be aware that you will have to go to Gatwick for the initial examination and it is not cheap.