Difficult one as you used to be able to do this, but now the law has been clarified and only a bailiff can execute a Warrant of Possession. Until then the tenancy has not ended.
Even if you were to make an unenforced entry i.e. using your key, then you could still be charged with unlawful eviction.
BTW it is not a Possession Warrant Notice, but a Possession Order that expires.
The advice I give should not be construed as a definitive answer, and is without prejudice or liability. You are advised to consult a specialist solicitor or other person of equal legal standing.