I phoned them a while ago for confirmation and they referred me to point 9 of their terms and conditions under the heading “Betting”. This says :
‘9.Minimum and maximum bet stakes
Depending on the product or type of market you are betting on and depending on the currency that you are betting in, there are minimum bet sizes that apply. These minimum bet sizes are subject to change and may differ depending on whether you are on our site or using the Telephone Betting Service. You are not permitted to place bets or try to place bets that are below the minimum bet size threshold and doing so may result in your account being permanently closed.
Your betting limit is represented by the lesser of: (i) your ‘Available to Bet’ balance shown in your account and (ii) your ‘Exposure Limit’ (which is available in the “Account Summary” tab in “My Account”). However in the event that we process an offer for a bet or the acceptance of a bet in an amount outside the applicable thresholds, such bet will nevertheless stand.’
Carry on doing it and they will warn you, then ban you if you persist.