The Lay Percentage Staking Plan is essentially identical to the Percentage Staking Plan used with Backing bets.
 
There is one rule that is followed – The stake used is a % of the cumulative bank. For instance, for a start bank of £2000 you would maybe use 2% of your bank making the stake £40. Your next bet would be 2% of whatever the next cumulative bank total now is.

In TSM there is are options to use a ratchet mode and to use the Last Bet filter to tell TSM when recalculate stakes.