Stay at home in the rain with the rest of us - that’s my advice

Can't you just ask them to re-route you and keep your booking?

Head for Points or Expert Flyer are the best places for these questions. 

I’ve just had alerts come through that my flights have been cancelled and I have been rescheduled to one leaving last thing at night and returning very early in the morning. Bastards. Looks like it’s a massive wait on the phone to try to get through to them to sort things.

https://www.citizensadvice.org.uk/consumer/holiday-cancellations-and-compensation/if-your-flights-delayed-or-cancelled/

Yeah so we are on a flight the next morning so that is not a problem, but because we need to collect the car the following morning than when we were due to arrive we have to change the car hire booking, which when we booked in January was £250 and now is over £700 and we are having to pay the difference..  

Airlines taking bookings then cancelling flights when not enough people book to make the flight viable is fairly normal at the moment.  It's really not worth flying around with 30 paying passengers on board.  

This is part of the 'new normal' of what to expect - and one of the reasons I won't be booking an overseas holiday until the Covid madness ends.

Ask on headforpoints daily chat. Some of the posters there are very knowledgeable in how to deal with BA. 

That seems ridiculous from car hire company, all you are doing is picking it up late, shouldn’t be any skin off their nose,

Good luck claiming anything beyond the agreed compensatory scheme linked to above - your car hire surely falls into the 'remoteness of consequence' category.

Rather than rebooking have you tried just dipping them a line saying you will be late picking up car?

Tell me about it, wasn’t even a cheapo one either purposely didn’t book a goldcar or other alternative shit one as I expect a better service when things like this happen booking a big name but clearly not. 

Thanks some good pointers here  

Have a look at the link.  If you're delayed more than 4 hours within 14 days of the flight you can claim between £220 and £520 per person depending on how far the flight was.  That is irrespective of actual loss.

Have you checked availability with other airlines? It may be cheaper to book another flight at a time that suits. If BA cancel the flights, you are entitled to a refund. If you are a member of BA executive club, phone the helpline number (they answer with a bit of a wait and some semblance of customer service which seems to be absent on the general customer service desks).