No support under the wall of kitchen extension

Don,t quite understand what you mean by a concrete sleeper i will presume that is a lintel bearing on the two flank walls and if it has been done correctly i.e enough bearing on the walls and the right size lintel for the load bearing down on it. That is no different that what happens at widow and door openings so long as it has been done correctly it will be fine and water incursion down the side of any building is the norm if there is no sign of any subsidance you can assume its been done correctly last resort you can contact local authority building control or planners to make sure the extension was done to regs! I would let it lie or you might end up in a legal battle with your surveyors when you bought the house if anything is untoward they should have picked up on it when you purchased the property. Not unheard of that they get it tottaly wrong i am no fan of all the know alls who think they can tell just by looking most of them know nothing about yhe buildings or how it is done i,d best leave it there before i talk myself into trouble. I think your alright with what youv,e got i.m.o

this may be where they have put a lintel over an existing drain run witch is covered in pea shingle or gravel.