Landlord came by without notice and unlocked all rooms

[A H]

Hi,

I've just come back from a three week holiday abroad to find my room unlocked and stuff moved around.

I live with 5 other tenants with locks on every bedroom door.

2 days after I left the landlord came by with a woman from a lettings agency and showed her the house and all the rooms. He didn't give any notice and he left all the rooms open.

I've called him for an explanation but he blatantly denies it and says he only showed the agency one bedroom.

There were two housemates in the house at the time so proving it shouldn't be a problem.

What can I do? I was hoping for an excuse but because he's now lying about it I want some sort of justice.

thanks in advance,

Aco

btw. this is in the UK (Hertfordshire)