Seemed to be pretty sensible advice given on the Lamm this year:
Adders are quite active at this time of year; however it is extremely unlikely that anyone will be bitten. Should you be unlucky, immediately wash the bite to remove venom on the surface, dispel any notion of continuing competitively and rest with the relevant limb lowered below the heart for about half an hour. Bandage the limb above the bite just tightly enough so that the veins below bulge but pulses can still be felt. "Milking" the bite area to expel blood and plasma could be tried too. If you are not feeling too feverish or nauseous after this rest, proceed gently either to the mid-camp or to a road, whichever is the nearer. Seek medical advice as soon as possible.

From http://www.lamm.co.uk/2017/event_details.htm