Home information packs could create a serious backlog in the housing market now the scheme has been widened to include more properties, experts are warning.

From today three-bed-room homes, which make up around two thirds of the market, join larger ones in requiring the packs.

HIPs must contain a report on energy efficiency as well as other key documents and fears are growing that London, which has comparatively fewer energy inspectors than the rest of Britain, will face particular problems.

An Evening Standard assessment of the five weeks since HIPs were introduced found no evidence of them damaging the market, nor of sellers or agents evading the rules. The penalty for putting a property up to sale without a HIP is £200 a day.

Estate agents' website Rightmove has found that energy assessors in London will have to carry out at least 48 inspections a month each to keep up with demand. This compares with only 14 per assessor in East Anglia, 26 in Yorkshire and Humberside, and 27 in Wales. The expansion of HIPs was criticised by law firm Wedlake Bell, which said the system was "already creaking alarmingly".

Spokesman Jeremy Raj said: "We are getting very panicked enquiries from sellers and agents who don't know where they should go or what they should do next." Miles Shipside of Rightmove said: "This will be a tough test for HIP providers and estate agents as it represents a massive increase in the number of properties needing one. "It will expose any shortage of energy assessors, especially in London where there is a busy market and relatively few assessors."

The move to extend the packs to three-bedroom homes has been welcomed by HIP providers, who have delivered more than 7,000 since the scheme was introduced for fourbedroom homes on 1 August. They say it is taking an average of five days to produce a pack. The average cost is £300.