A trade mark can only be effective if it is in writing and signed by the assignor (section 24(3), Trade Marks Act 1994. There is no statutory requirement to register the assignment at the Patent Office however it is a good idea to do so if you are the assignee ie the person receiving the trademark since if not it will be ineffective against a third party if you have to enforce it.

Importantly if you do not register an assignment within 6 months of the date of the transaction, the assignee ie the person receiving the trade mark has no right to its costs relating to any infringements occurring from the date of the transaction to the date of registration of the assignment.

Licences  

As with assignment under the Act a trade mark licence must be in writing and signed by the licensor. There is no requirement that a licence needs to be registered but if it is registered you are allowed to bring infringement proceedings in default of an action by the owner.

Both Licenses and Assignments do not carry any Stamp Duty