What does your contract say about viewings?
If it doesn't say anything, just refuse.
If your contract says you will allow viewings, your statutory (set in law) right to quiet enjoyment trumps that so you can still refuse viewings but, in theory, you might be liable for the landlord's losses if it delays the property being let.
If you are going to allow some viewings that doesn't give the landlord and agents the right to do viewings whenever they want.
You can set out reasonable rules eg
They have already taken photos and video, you don't have to allow them to take more. Presumably they also have the photos from when you moved in.
If you allow photos, they cannot move your belongings. You could also refuse to allow them to photograph your belongings.
Tell them they can only contact you by email to arrange viewings and you require at least 24 hours notice for access, as required by law. You can also set times/days when you are available for viewings, a limit on the number of days per week that they can come. ie they can't have a viewing every day for 7 days but they can have 7 viewings on 2 dates in the same week.
If you want to be there, specify that you will not allow viewings when you are not there.