Best answer by woz
PP can't take him on with that setup, he will need to have the meter changed and go to one mpan if he has two (which he almost certainly has, at a guess)
My advice is for your mate to talk to SP with a view to changing his metering to Economy 7 with one mpan (one supply), then give it a few weeks and switch. He should not take a tariff with PP which has a penalty for leaving if he does that, it may cost a little more but it will only be for a short time. He will then have the option of doing a comparison, but if he changes to PP the day and night rates are the same.
My mate has Comfort Plus Control white meter heating from Scottish Power, seemingly no other supplier will accept this type of tariff as it has three rates of supply. Normal domestic, cheap rate for nights and the third is a constant 24hr cheap rate for bedroom panel heaters and hot water. Im sure he said he pays 25p per normal day unit and 17p for the cheap rate. Any suggestions on an alternative tariff.