Tenant has vacated property without proper notice

Rent Arrears

A problem tenant who had run up at least two months arrears when pursued for rent finally texted me Saturday to say he wrote to me giving notice three weeks ago and sent me a key. The letter and key were not received (as yet).
Upon visiting the property yesterday I confirmed he has vacated the flat but left stuff in the yard and outbuilding but flat generally OK if dirty but needs refurbing anyway.
He wont answer my calls or texts.
The tenancy agreement had a two month notice period and the tenancy ran fron the 14th of the month holding over since 2008.
Based on his argument the notice was given on or about 1 August but he seems to have left about a week ago based on a conversation with the manager of the ground floor shop unit below the flat in question.
Is it safe to accept his premise but hold him to a notice period ending at the end of September or would the period be effective from 14 August therefore until 14 October? Or is there some statutory get out for him?
How should I pursue him? No forwarding address I dont even know who the utilities providers are and have had to change the lock and get a new gearbox fitted to the recently replaced front door. I think I can guess his new address but presumably tracing agents can confirm or otherwise within 24 hours.