You can hire them from the likes of HSS -
http://www.hss.com/g/49622/60m.html - but they don't come cheap!
It's probably cheaper to pay a specialist company to actually do the survey
for you - which shouldn't cost much more than a couple of hundred quid.
If you fancy a DIY solution, you could attach one of Mr Maplin's cheap 
cameras such as
http://www.maplin.co.uk/Module.aspx?TabID=1&ModuleNo=104962&doy=18m6 to a
drain rod, and stuff it into the pipe - with your end of the cable plugged
into a portable TV. [It comes with 10 metres of cable, and longer ones are
available - but you'd have to make relevant bits of the camera plus the
electrical connections water- (and other things!) -proof by binding them
with self amalgamating tape, or somesuch. It's not really designed for
unprotected outdoor use - let along being submerged in God knows what - but
would probably work for long enough to get a one-off result if you took
 Currently 40 quid, but often on offer at 20 quid
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which is waterproof and comes with a monitor. Might have to cut the weight
Google this group for this subject - it has been covered in detail a
couple of times previously. My dad built a lego vehicle and attached a
Maplin camera. Ended up with a really good system. All good fun!
Thanks for the tips Jon and Roger,
We hired this 'SeeSnake' from HSS for half a day in the end:
Very impressed with the way the 'rod' (a reel of very clever stuff that
feeds in and out of a holder like a tyre) went round corners that our normal
drain rods got stumped at. So, as well as showing that the pipe was
relatively clear, bar some clagg at the joins that the stiffer rubber drain
pusher would not pass, the SeeSnake enabled us to get a rope right through,
with which we could then pull the drain pusher through.
Before realising we could pull the rubber pusher through - by making a
couple of holes in it to take a piece of coathanger wire to make an eye for
the rope - we had made a wooden shuttle, from a piece of round fence post
with floorboard nails hammered in as scrapers, and holes for rope attachment
at each end. This we pulled back and forth to loosen any detritus - but it
turned out there wasn't much to move in the end. The SeeSnake proved an
excellent device for putting one's mind at rest (Note that it can be
confusing working out which way up it is, but you soon get used to it.) and
might even be worth having one's own...
Roger, that link about the cameras, reminds me I have been meaning to look
into DIY home security, but, as there seems to be a very confusing amount of
kit out there - some of it hugely expensive - I had not got very far with
deciding what we needed and what to buy. I would imagine this is another
Ta very much to all,