I need to know the legal requirements for saftey/emergency lighting in flats - we have had an expensive quote to bring blocks up to date but do the new legislations only affect new builds ie. not existing ?

No the legislation affects the common areas of all builds but the question you need to answer is do you need emergency escape lighting. If the normal electric supply failed during a fire in the hours of darkness is there sufficient borrow light from out side the premises to enable the tenants to find the way out of the building safely, if there is, then you do not need EL. Check it out with your fire risk assessor.

The first point of call for "do I need it" is without doubt your fire risk assessment, it is worthwhile & can save you making expensive mistakes or being "miss-sold" unnecessary equipment.