However, sections 11B and 11D do not apply to a contract to do residential building work or specialist work in circumstances that--
(a) if the work were not to be done promptly, there is likely to be a hazard to the health or safety of any person or to the public or to be damage to property, and
(b) the work could not be done promptly if the requirements of the particular section were to be complied with before commencing the work.