Hi, did a little looking up for you as was curious myself. Anyway I found this and it might help you. This is an excerpt (sp?) from the consumer affairs page.
If the tenancy agreement is a fixed term agreement the landlord or agent cannot increase the rent before the end date, unless the agreement states otherwise.
In any case, a landlord or agent must not increase the rent payable under a tenancy agreement more than once in amy 6 month period.
The landlord or agent must give the tennant at least 60 days notice of any rent increase using the 'Notice of Rent Increase to Tenant/s of Rented Premises' form.
The way I read this is that the owner is in his rights to increase the rent, as you will be entering into a new contract after the 1st August. However I think that the agent should be giving you one of those forms soon, as 60 days isnt far from the 1st Aug! Try going to the consumer affairs page, there is a list of email addys that you can send this query to and they should be able to give you the right answer.
DD1 July 2004 DD2 August 2007 DS September 2009