The body that protects you against bad practice is ARLA- that is, if Willmots are members. There used to be Private Tenants person in the Council- you could try them also.

You could also try and communicate directly with your landlord, as it is they with whom you are in contract, not Willmotts. Address a letter to the owner, post it to yourself, and then pass it to Willmotts for forwarding on to the landlord. They may not be happy either with bad management practices as effectively Willmots are putting their income at risk. It may also not be their idea to put the rents up. Additionally it may be someone junior at Willmotts thats making all these gaffes. You could try and speak to a senior partner. From experience, a lot of estate agents take on the letting and management function without training their staff in good and legal practice.

Generally rent increases can only happen at renewal stage ie you are bound to pay an agreed rent for an agreed period. To put the rent up during the term is a variation of terms which can only be done if both parties agree. What term did you take the property for?
I am not sure whether open market rents have the same protection any more, pr whether its relevant as to what others pay for similar properties, but best of luck if you can challenge this. I think the renewal cost of ?45 is probably standard and is somewhere in your terms and conditions.

They have a right to send contractors in in emergency situations such as leaks etc, especially in flats, however it is generally both breach of contract and breaking the law ( eg harassment) to enter a tenanted property without notice and to do works causing damage, etc. They sound like they havent a clue how to manage.