I cannot answer you fully and accurately without seeing the lease. Therefore, going to have to make some assumptions.
Assuming that this is a properly drafted lease, the landlord doesn’t have to collect the rent. You are under a duty to volunteer it whether he demands it or not. That is of course assuming that the lease is a properly drafted lease.
As soon as you stop paying the rent, you fall into arrears. As soon as you are 14 days in arrears, the landlord can foreclose on the lease and lock you out without actually applying to court. That is the provision in the lease.
It may be that the lease is defective or inadequate or that provision is not in there in which case the landlord would need to apply to court for an eviction order. That might be why he applied for the order or he may not have been aware that he was able potentially to evict you without. However if there is a forfeiture clause in the lease, which you say there is, then he didn’t need to go to court.
Under the 1954 act you have a statutory right to a new lease under the same terms as the old lease albeit at the market rent. He can refuse to grant lease on certain conditions and in this case he would only have to pay you compensation for taking back the premises if he intended to redevelop it himself or occupied himself and he had firm and settled intention to do so. A sale of the premises is not one of those conditions.
The reason he is claiming mesne profits and not rent for this latter period is because if he was claiming rent, you can claim that you had a tenancy and were entitled to remain in the premises. Financially it’s the same but it’s a technical point. His legal costs are whatever they have cost for the solicitors who will have charged about £200 per hour plus any court costs. A fee of £4000 is probably about right.
I assume that you defended the landlord’s action and lost. You can only appeal if the landlord made an error of law or an error of fact and on these facts, he made neither. You admitted that you have paid rent albeit that was because the landlord did not collect it but as I have said already, that is not relevant. You didn’t pay rent and hence, at the time of the judgement you were in arrears and the landlord was entitled to possession.
I’m sorry, I wish I could give you a more favourable answer but it’s the non-payment of rent which has been the problem for you. If you had continued to pay rent regardless, the landlord would be unlikely to have got the order against you.
Can I clarify anything for you?
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