What are the consequences of not fulfilling an undertaking?

An undertaking given by a solicitor is enforceable by the Senior Courts.

Failure to comply with an undertaking can lead to disciplinary action being taken against the individual, and the firm, by the Solicitors Regulation Authority. If you fail to fulfil an undertaking, you may also be subject to disciplinary proceedings by CILEx Regulation.

The recipient could also bring an action for breach of contract.