Completion and the CGT exemption

If a property is auctioned off end of next week, how soon is completion likely to be for the purposes of the CGT exemption - which winds up at the end of the year? Is it a case that if contracts are signed this side of the new year, then the buyer and his new property will qualify for that exemption - or does the sale have to be completed in full?

CGT acquisition and disposal dates run from the date of an unconditional contract or, for a conditional contract, the date on which the last condition is fulfilled. If the exchange occurs and all that remains is the effluxion of time and payment of the contract sum for completion, the acquisition date will be the exchange date. If completion is conditional on something such as receipt of retrospective planning, it would be the dat eon which such permission was granted.