1. The office lease you signed is effectively continuing twelve month rental periods with only the option to break the lease arising on 3rd September each year. So I regret to say that youare tied in for another 12 months from this September as you did not give the necessary 3 month notice period on 3rd June of this year. Secondly, it is correct to say that you can assign the benefit of the lease to some third party. This is another way to bring your obligations under the lease to an end as then someone else will be stepping into your shoes to fulfill your obligations under the lease. So you can advertise the lease with an estate agent and get someone else to come in and finish off your obligations for the remainder of the 12 month terms which is outstanding. Otherwise you will remain liable for the rent due until 3rd September next year.
2. Be aware that there is no requirement that you be told that the lease is continuing for another twelve months. You are taken to have read the lease when you signed it. So it does not matter that you received no email telling you the lease would be continuing for another 12 months. When you signed this lease, you failed to realise how heavily skewed in favour of the landlord the actual terms are. Finally, I regret to say that there is no way in which you can bring your obligations under the lease to an end before September 2015 apart from assigning the lease.