Note if this conversion has been done properly (probably not) then there are many things the landlord should have done, to do with safety, health etc. including maybe smoke alarms, fire doors, adequate toilets etc.
I would report it to the council (not sure which department) and get them to go round and have a look.
p.s. Another great example of why being in the EU is such an awful idea.
Many sheds and garages and other dwellings are being built at the back of people's houses and rented out to illegal immigrants, many without toilets, running water etc.
http://www.dailymail.co.uk/news/article-2362393/Inside-migrant-Shed-City-Immigrants-living-cramped-illegally-built-garden-sheds.html