Monthly bill now at approx £500!!

markin

If the air con has heat it will be at least x3 cheaper than the oil heater, putting the oil heater on a timer for night only would be a quick fix and also rise the set temp on the ac so oil comes on less.

Devide their total meter reading by total days to check how much they have been under paying, and start taking weekly reading if this is the first winter?

frederick1950

If you have been 'reasonably' happy in the past with. £100/month contribution then even on the last and next rise in the SVR they should be paying at least 70% more.
Why should you subsidise them ?

JJC1956

Why don’t you gather up a pile of bills and drop them off to your mother to let her peruse at her convenience, if they don’t shake her up a bit you have a problem.

pallyman

Is the £100 they give you including water rates or are they paying towards it separately,Also would it be possible to share food costs & maybe batch cook to save costs.Maybe even wash for both households so you are doing a full load,but they need  to pay more for power..

Brie

When we set up our home with MiL I did a tally on the bills and told her what her share was to be.  Didn't ask.  Told.  And it's gone up as costs have gone up as otherwise we'd be in the same situation as you.  I also am quite happy to go in and turn off her heat, lights, TV.  Her lounge will be absolutely tropical, all the lights on, TV at top volume.  And she's sound asleep.  I've also told her weekly carer to ensure she's in a jumper or if she insists on a tshirt that there's a cardy over it.  I get that she sits and does little and so gets cold but there's ways to manage it. (mostly)

QrizB

@JSCM there has been a lot of good advice in this thread. Some of it a bit harsh, perhaps, but all offered in good faith.

GingerTim said:

Install a coin-operated meter so they appreciate how much electricity (and money) they are burning through.

I was going to sggest something a bit more 21st-Century, how about a PAYG smart meter?

https://www.topupmeters.co.uk/

Your parents pay the meter company and the meter company pays you.

JSCM

Thank you all for your input. I’ve got a lot of thinking and talking to do.

QrizB

While you're thinking: if you know how much electricity your annexe used during the last billing period and tell us, we can estimate how much it cost you.

Gerry1

Why not investigate the garage having its own independent supplies?  They would just pay their suppliers directly so subsidising them would no longer be a problem.

If it's relatively straightforward you wouldn't even have to tell your parents that you'd instigated the change, you could let them assume it was as a result of being in a different property for council tax, or whatever.  Or perhaps find a tariff that's better suited to them, one that requires a smart meter but say you don't want one so they'll need to have their own meter in the garage.

Sea_Shell

JSCM said:

Thank you all for your input. I’ve got a lot of thinking and talking to do.

@JSCM

Have you had a chance to have the big talk with them yet?

If so, how did it go?