As the council are pulling down all the flats in the area, are they pulling down yours as well in the future? If so, then you would be entitled to receive a sum of money from the council, although I don't know how much or how compulsory purchase works.(posted 8353 days ago)The aftermath of handing back the keys voluntarily and having a repossession forced upon you is the same.
I would suggest that you do see a solicitor for advice, if not for the repossession/surrender, but where you stand with the council and their demolition plans.
If the council are not planning to demolish your block, you may be entitled to some sort of compensation for having the flat devalued because of their actions. Only a solicitor can advise you on this.