The Sonderkündigungsrecht should be a break clause in the UK. From the Shelter link below:
"Using a break clause to end your tenancy early
A break clause allows you to end the tenancy before the end of the fixed term.
If your tenancy agreement contains a break clause, it will say:
when the break clause applies (such as 6 months after the tenancy starts)
how much notice you have to give
You don't need your landlord's permission to use a break clause."
[Edit:] One example:
"The tenant gave a break notice to end the lease on 24 January 2012."
http://www.bowlinglaw.co.uk/rental-payments-after-break-date...