"I currently have a 10-year lease which is due to expire in 2014. The lease is a renewable one with rent reviews every three years. It has a fixed increase of £600 every three years, ending at around £10,500 per annum in 2014.
"My question is, when I renew the lease is there something in law to say that the lease should carry on from the current rent, or can the landlord start from any amount of rent he likes (he is currently suggesting a start rent of £12,000 with an increase of £1,000 every three years)?
"Also, is there a fixed method of assessing rent as £x per sq ft or dependent on rateable value?"
I can't answer legal questions for fairly obvious reasons but I would say that all contracts are negotiable to some degree. The 'going rate' is a useful benchmark and an upwards-only rent review is common, but also negotiable. Terms of business leases are much less standardised and so, yes, negotiable. To summarise: once you find your ideal place (location, location, location) then agree the terms (negotiate, negotiate, negotiate).
You are probably not equipped to do this or you would be a chartered surveyor rather than a retailer. To find one, and a free half-an-hour on the phone, ring the Royal Institution of Chartered Surveyors on 0870 333 1600. The theory is that a surveyor should save you more than enough to pay their fees.