tenants wont leave after notice period

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Hi I am a private land lord I have recently moved from Sheffield to Worthing to be near my son. I own a house in Worthing but is currently let out. I have given my tenants notice to move out by July but because of change in their personal circumstances I ma concerned that they may no move out. I want to explore my rights in this situation because I am currently living in Airbnb with all my belongings in storage and my son has LD very stressed as he cannot understand why I cannot have him for weekends. Please can you advise what to do in case they do not move by July? I do not have any written contract with them as the one we had from the estate agent expired and decided to go privately