Selling plot

I posted before about selling part of my garden to pay for work on my old house.
Last week I got planning permission and decided to sell at auction but have just found that there are restrictive covenants on my deeds. They were put on when the council owned the house and now belong to Aster Housing, who charge an absolute fortune to remove them. Greedy bastards!
Anyone owning an ex-council house should check their deeds, I wish I'd known this before I started, I could lose a third of the selling price on top of all the other massive bills involved.