If you plan on subscribing, you should remember that you also need to have a copy of the game (which you can buy on the official website for £10). You can't just start paying the sub from a friend trial.
It's also worth pointing out that the Steam Christmas sales are likely to start tomorrow and if STO is discounted, that comes with a 30 day sub, 500 points and a few extras.
I already access the game via steam as I added it via the old 'add a non steam game' as I find the steam chat etc invaluable to keep in touch with friends whilst gaming.
I'll have a look what Steam offer. Thanks again everyone for your replies