Hi mate thanks for your reply.  
Think I've got my explanation wrong slightly, I had thought a martingale on a lay of 1.2 would just add the previous losses?  
In the same way that is what the principle of a roulette martingale does at odds of 2.0, but using a lay of 1.2 the stakes would increase at a much slower rate.
So would look like this...each step recovers loss and wins initial stake...
Bet 1 :   10 @ 1.2 = £2 liability
Bet 2 :    12 @ 1.2 = £2.40
Bet 3 :    14.40 @ 1.2 = £2.88 
Bet 4 :     17.28 @ 1.2 = £3.46
Bet 5 :      20.74 @ 1.2 = £4.15
Is there any way the trigger you've designed me could be altered to the above?  I understand if I need to wait for more free credits. 
I have tried making the above staking plan by simply setting a lay 'default_lay+prev_lost' but it was picking up all losses on account I think rather than from within this trigger. 
All help appreciated.  Thanks McBee 

Rob