There is the well-known problem of Abandonment

How can a landlord prove it ?
We know the telltale signs that your tenant has abandoned your property, non-payment of rent, no sign of tenant, only rubbish left behind, other neighbours have told you what has happened, gut feeling, but how can we prove it to a court's satisfaction

Back in 2004 the Labour government refused to add  proof of abandonment to the 2004 Housing act and they actively fought against it, making the law deliberately obscure and very confusing

If a tenant claims they did not abandon the property (and they obviously did)  It’s ridiculously difficult for a landlord to defend against and the punishments are quite severe as the the law considers it to be a wrongful eviction

RenterBall’s Solution
So your tenant wishes to move and not inform you (abandonment)
They see the new landlord using RenterBall and they are stumped

They can’t just abandon your property

For them to be able to sign a new RenterBall agreement with the new landlord they first need to have received (No debt) feedback from yourselves within the last 35 days

This stops abandonment in its tracks as the tenant is forced to contact you to get feedback
This gives you the landlord the opportunity to leave debt feedback. If you leave feedback declaring your tenant owes you money and you haven’t put them on a payment plan then they are blocked on RenterBall from being able to sign a new agreement

For the more sneaky and deliberately malicious tenants they can request feedback and if you happily leave it, they can then sign a new RenterBall agreement with the new landlord and move but they deliberately do not cancel their tenancy with yourselves

Just because somebody is renting a new property legally doesn’t mean they can’t keep yours, although some tenancy agreements state that it must be your tenant's primary residential property. 

Nothing says they can only have one rental, however by knowing where they have moved to it allows you to pursue them for the rent, and just because they have moved doesn’t mean they are no longer liable for the rent. At least you can get a Surrender Notice signed by them so you have good protection from an unlawful eviction claim

Legally, until your tenant tells you they have left or a bailiff has given you the property back the tenant is still liable for the rent