Note that I'm not an expert by any means and I've just got this information off the net
and from the Woodsmoke people and am just passing it on.
You can search for tick, ticks, Lyme, Lymes etc for further threads on this topic.
Ticks can carry a number of nasties including the bacterium
Borrelia burgdorferi
which can lead to borreliosis or Lyme disease (usually called "Lyme
's Disease"):
http://en.wikipedia.org/wiki/Borrelia_burgdorferi
http://en.wikipedia.org/wiki/Lyme_disease
As far as I'm aware if the tick is spotted and removed promptly (and correctly / safely)
your chances of getting infected is low in the UK. If you do notice symptoms get thee
to the doctor and go on a course of antibiotics. The symptoms can be a troubled looking
bite area, possibly with an expanding rash and flu-like symptoms. Some people have
suggested that the symptoms aren't reliable and if you've been bitten you should get
antibiotics anyway - but this seems a bit impractical. Maybe some sort of judgement is
made relating to the estimated time the tick's been on you and its size - apparently
larger ones are more likely to have fed on something before feeding on you and so might
have picked something up. If they're really tiny - you might have been the first meal.
Without treatment things can get a bit nasty as it can affect the nervous system but in
the initial stages it seems to respond to antibiotics.
Apparently there is a danger that if the tick isn't removed with care then it might
regurgitate some of its stomach contents (= your blood meal + bacteria) into the bite
which increases your chance of infection - this is why you have to remove them with
care.
There's a very good website that highlights things to be aware of tick-wise and will sell
you the little O'Tom tick removers (they work brilliantly I've found) which extracts the
beasties from your body.
http://www.bada-uk.org/
Some people recommend hanging on to the tick in case of infection as it might be of use,
probably to epidemiologists though possibly in diagnosis - I'm not really sure why!
Ticks seem to like some people more than others, may or may not be discouraged by
repellents but tucking your socks into boots might help.