The base game isn't massively focused on British rolling stock, it's mainly German, you would need a number of mods in order to get more modern British rolling stock.
TF2 is just a slightly visually enhanced TF1 in my opinion and not worth the price difference between the two. The base games are pretty similar. My advice would therefore be to try TF1, see if you like it for an hour or two and if you don't then get a refund from steam and you haven't lost anything that way. If you do like it, get a refund for TF1 and then get TF2 instead.