Is this lawful

[Hellobee]

A council landlord increasing rent soon after tenancy was signed mid year and saying they made an error. Housing officer confirmed three times in emails what the rent was prior to moving into the property than rent account was increased. Council are insisting there was an error regardless of what the tenancy agreement states.

Is this lawful?

Doesn't sound like it

I think rent can be increased at six months when it is possible to issue a new tenancy agreement. Maybe try posting in Legal Matters.