Your problem Threemae is dependant upon the nation, or even the town and city you select. This is why you have to define whom you mean, where and when.
There are regional differances in the UK, and there are differant mortality cuases, for example in the Lancashire and Yorkshire towns of Northern England you’ll find lots of respiratory problems due to the cloth mills and coal mines, in the rural uplands of Scotland or the agricultural market towns such as Ripon you’ll find other problems.
Then, added to all that, is the quality of record keeping. Some of the best records are those of the clergy, however these simply do not reflect the mortality of the population at large. In some cases figures for boroughs are not comparable year by year because of boundary changes.
British Historical Statistics is probably one of your better options as it gives breakdowns by age - death rate per thousand and by region, but AFAIK not by occupation. You would need access to a University library, or be prepared to pay a significant wad to obtain a copy, it can be found on google books but you will need to be patient and persistant to get it into a usable format.
Despite all this, there is enough evidence to generalise that around 40 years was pretty much the limit for the majority of workers, and these were the majority of the population - some towns were much worse, Bradford for example was noted for being very bad for lifespan.
In the UK during the 20thC our records are very much better and lifespans have increased from around 45 for males in 1900 to around 75 for males in year 2000. We can take these as reasonably accurate.
Something worth bearing in mind is that the figures from 1800 to 1900 will be worse as public health reform was only enacted around 1842 and it took some years before the effects were felt, when comprehansive sewage and water supply systems were steadily introduced and these were ceretainly not fully inplace by 1900, it took another 50 years before anything like a modern service for water and sewage was properly operational in the UK, and another 20 years more than that before you could truly call it comprehensive.
Chadwicks reports published during the 1830’s onwards gathered some information about death rates and they certainly caused town councils to invest in such sanitary arrangements, pushed by the cholera outbreak of 1848.
Here is some more easily digested research that can be used to justify the 40 year expected lifespan at birth.
http://www.parliament.uk/commons/lib/research/rp99/rp99-111.pdf
look for pages 8, 9 & 10
I also must point out that lifespan and life expectancy are two differant things.
If you know what you are talking about, then yes, you can make a very good case for saying that life expectancy in the UK between 1700 through to 1880 was around 40 years for men. You can even make a case, though weaker, that the lifespan for UK males during this period was also 40, its true that some men lived longer, but not many in comparison to the population as a whole.
If you read the links I have posted then these will give you some idea of where to begin to look.