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Hi thank you for your patience. He should have sought your agreement first. It is trespassing and if he has not finished yet you can stop them either by simply telling them or by securing an injunction order against them. They should have asked you for permission and if it’s necessary work and you had refused they would have needed to apply for an Access Order to be able to enter your property to do their work. I hope this helps and I would be grateful for your rating at your earliest convenience. All the best.
Nothing really unless he has caused some damage in which case you can pursue him for compensation. You needed to have stopped them whilst the work was ongoing.