Being Evicted from a periodic rental basis

[Crosbie]

We have now passed our fixed term tenancy period and we are now paying rent on a periodic, month-by-month basis.
Our Landlord allowed us not to pay December 2008 month's rent because of on-going problems in the flat since May 2008 of which the property management agents of our flat had failed to fix after constant chasing from us (the Tenants). So we cancelled our direct debits for December and we haven't yet reinstated them because some of these problems have still not been resolved completely. We notified our management agents about these problems at the time when they told us the jobs in the flat had been completed.
Where do we stand if we send an email to our management agents, copied to our landlord, stating that we are not paying rent until all the problems are resolved, otherwise there will be no end/completion to these issues. I don't think they can evict us for that as its their fault these problems haven't been resolved as we were constantly chasing them about each issue? But however we are worried that they could just severe us with a months notice as we now pay rent on a periodic basis. Surely all they have to do is make some sort of excuse? For instance the Landlord could say he wants the flat back for himself or family to live in? So would we then have to leave?? Or do we have more rights to say we want to stay? Do we have enough ground to stand on not to pay Jan month's rent? Or is it too risky because we could be served a months notice and have to leave the property??