206doorman:
Happy Keith:
Hey, a pukka chance to wear tights?I wear tights in winter. Perfect for those very chilly days. Surprisingly comfortable too!
Yikes; ‘…perfect…’?
Moving on…
I got this reply from the HSE today, Basically saying the employer has to provide you with the correct PPE to do the job. If you are cold then they must supply you with some PPe to keep you warm. So say bye bye to a night heater but hello to a nice new fleece or overcoat. 
HTH
Dear Sir
Thank you for your enquiry regarding temperature requirements for outdoor workplaces.
There is no minimum/maximum temperature set down under health and safety regulations which relates to outdoor workers. However, section 2 of the Health & Safety at Work etc Act 1974 places a general duty of care upon employers to ensure the health, safety and welfare of all employees at work. In addition to this, all employers are required to assess the risks to their employees health, safety and welfare from work activities and put into place precautionary measures to reduce those highlighted risks. Risk assessments are a legal requirement under the Management of Health and Safety at Work Regulations 1999.
Regulation 3 stipulates that:
Every employer shall make a suitable and sufficient assessment of -
(a) the risks to the health and safety of his employees to which they are exposed whilst they are at work; and
(b) the risks to the health and safety of persons not in his employment arising out of or in connection with the conduct by him of his undertaking.
The associated Approved Code of Practice states:
This regulation requires all employers and self-employed people to assess the risks to workers and any others who may be affected by their work or business. This will enable them to identify the measures they need to take to comply with health and safety law. All employers should carry out a systematic general examination of the effect of their undertaking, their work activities and the condition of the premises. Those who employ five or more employees should record the significant findings of that risk assessment.
A risk assessment is carried out to identify the risks to health and safety to any person arising out of, or in connection with, work or the conduct of their undertaking. It should identify how the risks arise and how they impact on those affected. This information is needed to make decisions on how to manage those risks so that the decisions are made in an informed, rational and structured manner, and the action taken is proportionate.
A risk assessment should usually involve identifying the hazards present in any working environment or arising out of commercial activities and work activities, and evaluating the extent of the risks involved, taking into account existing precautions and their effectiveness. In this approved code of practice:
(a) a hazard is something with the potential to cause harm (this can include articles, substances, plant or machines, methods of work, the working environment and other aspects of work organisation);
(b) a risk is the likelihood of potential harm from that hazard being realised. The extent of the risk will depend on:
(i) the likelihood of that harm occurring;
(ii) the potential severity of that harm, i.e. of any resultant injury or adverse health effect; and
(iii) the population which might be affected by the hazard, i.e. the number of people who might be exposed.
Reference: L21 The Management of Health and Safety at Work Regulations 1999: Approved Code of Practice and Guidance, ISBN 9780717624881, £8.00.
If you are working outdoors on a construction site, the Construction (Design and Management) Regulations 2007 states the following:
Temperature and weather protection
43(1) Suitable and sufficient steps shall be taken to ensure, so far as is reasonably practicable, that during working hours the temperature at any indoor place of work to which these Regulations apply is reasonable having regard to the purpose for which that place is used.
(2) Every place of work outdoors shall, where necessary to ensure the health and safety of persons at work there, be so arranged that, so far as is reasonably practicable and having regard to the purpose for which that place is used and any protective clothing or equipment provided for the use of any person at work there, it provides protection from adverse weather.
I asked an old boss if the night heater on my lorry could be fixed as winter was starting to bite.
“I want you in at three tomorrow,it’ll be sorted by then.”
Went in the next day,jumped in the cab to find two tartan travel blankets on the bunk! 
If you have to lock the cab and surrender the key’s a night heater would be as much good as a chocolate teapot.
PPE is a last resort, other options must be investigated first, porta cabin, place to keep warm within the prison etc.
Why should a day cab truck not have a night heater in the 21st century? Saves running the engine wear & tear, and a host of other environmental considerations.
Relatively cheap to install with a quick return on investment.