As a landlord if you accept a notice from your tenant to break the lease, and tell the tenant this, then you will not be able to draw back from that position and deny the validity of the notice. A court recently held in circumstances where the notice had been sent to the former landlord who had sold his interest to a new landlord. The notice had been passed on to the managing agents for the new landlord who wrote to the tenant saying "We accept the attached letter and can confirm we are happy for you to break the lease".
When the landlord decided that he would prefer to have the lease continue he refused to accept that the break had been effected, but the court decided that the notice was sufficient to break the lease.
The lesson to learn is that it may be preferable, from the recipient's point of view, never to acknowledge the validity of a notice. If you receive a notice then consult your solicitor but do not confirm the notice is valid without advice. You may want to respond to the giver of the notice: "We acknowledge receipt of your notice dated ... with nothing further or add "but we make no comment on its validity"