A £100 bank? Good luck...
You'll be surprised how much money it takes to do matched betting. Place a £20 bet at odds of 4.2. Lay it at 4.0. That's your £100 gone, tied up until the bet is done. If it's a "qualifying bet" you'll make a small loss (to gain a free bet later). If it's a free bet, you'll make about £15 profit. £100 is doable, but it'll be slow progress and you'll need to reinvest your winnings.
I started with £300 mid way through the Euros. Now got a £1k bank, which makes life a lot easier. I had about £800 out over the weekend, for a profit of around £150.
I learnt from Matchedbettingblog.com, but made a number of mistakes early on that reduced my profit. I'd recommend joining OddsMonkey (the site I now use) or (because I hear good things) Yesbets, and work through the sign-up tutorials.