Mentioned these before- " NUNN TABLETS " dissolve 1 in 500ml water , seem to work for me.
Tubes of 12, various flavors, use as required.
Mainly known & used by runners.
Can but try, may help.

A very cheap and simple answer is common salt. Found in crisps, salted peanuts, salted cashew nuts etc. Tastier than electolyte drinks and gives some nice chewing sensation, and oils,fibre as well! Sometimes the diet needs salt especially if doing you are exercising more than you are not used to- and solid food such as salted nuts is good and maybe more satisfying than the electrolyte drinks except if you a runner of course! Then you may well need them.

Thanks folks for your replies, I will try the power drinks and just keep going. As for David I too get problems on stiles, and when tying laces sometimes - seems like my muscles are saying "lay off, you haven't used us for quite a while!" Then again, I go for months without a problem

I am sure that John is not the only one that has suffered from cramps, I do for one but in my case I seem to have them for several weeks and then they disappear for months. I am equally sure that John like the rest of us who have suffered the torture (mine seem to come on as I am descending hills or climbing stiles) will have checked the internet for answers and probably come to a negative conclusion.
Maybe one or more of our esteemed Doctor members or practicing physiotherapist could give us all some advice on how to deal with this horrible thing.

Wikipedia definition of cramp is "Cramps are unpleasant, often painful sensations caused by muscle contraction or overshortening. The most common causes are low blood sodium and potassium levels, accompanied by excessive dehydration. Cramps can also be caused by cold, overexertion, or a low calcium blood level (especially for adolescents, who need calcium for both blood and bone maturation). Illness or poisoning can also cause cramps, particularly in the stomach, which is referred to as colic if it fits certain characteristics."

My experience of cramp has been shortage of salt following periods away from home eating out - that food has salt added, which is not normal for me - I never use it when cooking at home. So when I come back to the salt free (or very low salt) diet at home, possibly combined with being a bit dehydrated out running, is when I get it, thankfully rarely.

I only get this in very hot weather, so I normally take a couple of those sports electrolyte sachets to add to my water which seems to do the trick. The addition of electrolytes also seems to help me absorb fluid rather than it going straight through. If this is one of your first events it tends to improve when you do them regularly. Hope this helps and good luck on your next event!

On the Hebden a week or so ago,admittedly a fairly strenuous walk with several early ascents, I experienced cramp in my thighs, both legs. This recurred throughout the walk from about half-way onwards. I took plenty of fluid, so what can I do on this, is it loss of electrolytes? I guess there must be a simple answer, it's just that it's new to me.