In this case, a party (guarantor to the lease) argued that the tenant had surrendered its lease automatically by 'operation of law', and the landlord had, by its conduct, accepted that surrender.
The High Court found that looking at the landlord's behaviour as a whole, it had not accepted the surrender; it had merely been protecting its interest in the property
The case? Padwick Properties Limited v Punj Lloyd Limited  EWHC 502
A landlord wishing to avoid allegations that its conduct may amount to acceptance of the surrender of a lease should ensure it has records showing, for example, why it is accepting the return of keys and on what terms, and should respond to letters and record phone calls to make its position clear.