What are my options in selling up

Currently using a managing agent (Haart) for a rental property. Coupled with difficult tenants, mortgage deal ending next year and simply a lot of hassle for not much in my pocket after tax and expenses, I want to sell up.

I would like to have a vacant property for sale but I'm in a 2 year contract via Haart with the tenants ending in October this year. I have to give 3 notice period which I plan to in July but I am conscious that the renters reform bill might come in before then and I just want to get ahead of that to avoid any extra hoops to jump through as I believe the tenants wont accept the eviction.

Is it possible to end fixed term tenancies early or do I have no grounds to do so?

As a side note, anyone looking for a managing agent, don't use Haart. They offload everything to a central call centre in Colchester regardless of location, use contractors with astronomical fees and the 'local' estate agent is nothing more than a shop front for sales.