I would be interested if anyone has any information why a lift shaft in single story buildings can not also serve the basement and/or have any thoughts on any compensatory measures that would allow the lift to serve the basement.

The issue is a small development of flats (10 flats on the ground, 1st and 2nd floors). There is a basement used for parking. The car park is classed as a covered car park even though there is vehicle access from the road (the flat ground floor entrance is up a steep hill from the pavement). As there is a requirement for 10% of flats to be 'accessible flats' so access to the parking area is essential.

BS 9999 16.72 states 'a lift should not be continued down to serve any basement storey if it is in a building served by only one escape stair.  

BS 9991 does not appear to broach  the subject.

ADB 5.44 states A lift shaft should not continue down to serve a basement storey if it is; in a building (or part of a building) served by only one escape stair and smoke from the basement from a fire would prejudice the escape route...?

Is ADB saying if the lift shaft is suitably enclosed in a protected shaft with FD60S doors and approached on the ground floor by a smoke lobby it is acceptable?

The covered car park will have mechanical smoke extraction to the correct standard, the staircase will be separated between the basement and ground floor, the proposed lift shaft will not be within protected staircase (both will be approached via the same protected lobby on the basement level), it is proposed that the protected lift shaft will be  120 minutes fire resistant with FD120S doors and the basement lobby to the lift shaft either mechanically vented or pressurised.

I personally believe this will provide suitable and sufficient protection to the escape routes from upper floors and am at a loss as why a lift shaft should be treated any differently to any other protected shaft as long as suitable and sufficient protection from smoke ingress is in place. I would be interested in other fire professionals opinions.

Reading your description I would think it meets the requirements of 5.44 of ADB but before giving a definitive reply I would need to see a detailed drawing. Has it been thrown back by building control and if so, for what reasons.

I do not think they are, providing smoke from any fire in the basement does not affect means of escape from upper floors.