UK Landlord Forum / Life

We have a solicitor working with us and she has sent the 2 occupants a letter advising them to hand the keys in by a time and date and because the are classed as excluded occupiers, so if i dont get the keys back then i can change the locks to regain possession. Technically they are residential squatters, therefore, i do not require a possession order.
My question is - i have never done this before, are locksmiths allowed to do this and is there a recommended firm i can hire.