Property lease review

I undertake voluntry work for a Chairty group and seeking assistance with regards our lease committments etc with regards one particular property. Its a lengthy document - 45 pages that i can send through to any interested parties PS - not a lot of money to spend on this project assignment!

It is dated from December 2008. We had work done to the building and did not actually move in until March 2009. The lease has not actually been signed.
They have written to us on 28th October giving rent demands for year commencing Dec 08 and Dec 09 and Dec 10. They are saying the rent was increased by 2% from Dec 09 and we should have increased our payments. They have not written to us about this.
I would appreciate some interpretation of the lease on the right to raise the rent without consultation, and secondly, our right to renegotiate the rent in the current economic circumstances and because we are losing 28% of our income next year as part of the government spending review.