Simply, I take a bet with even odds or higher,
this can be a single or a double bet,
the important thing is that the odds are 2.00 or higher.

Then I start with a £100 bet on my selection.

If I win, I bet again my £100 + the winnings = £200.
(MY BANKROLL = 0)
If I win, I bet only £300 and take £100 into my bankroll.
(MY BANKROLL = + 100)
If I win, I bet only £400 and take £200 into my bankroll.
(MY BANKROLL = + 300)
If I win, I bet only £600 and take £200 into my bankroll.
(MY BANKROLL = + 500)
If I win, I bet only £1000 and take £200 into my bankroll.
(MY BANKROLL = + 700)
If I win, I bet only £1500 and take £500 into my bankroll.
(MY BANKROLL = + 1200)
And so on ...

If lose, I start again with 100 - 50 - 10 depending of my bankroll.

The advantage of this system is that you can lose only in the
first 2 bets, after that you can't lose anymore.