Mercifully, I have never found myself short of water when crossing a desert, and I have not therefore, had the experience of seeing a pool of water that turned out on closer inspection to be nothing more than a mirage.

But I have frequently experienced a minor equivalent when walking down roads in West Dorset at election time.

As a politician who is short of votes, one has a distinct tendency to imagine that any placard of the right colour denotes an ardent supporter, even if it turns out on closer inspection to be no more than an estate agent's sign.

Somewhat similarly I experienced a slight thrill upon reading recently a headline referring to Bridport as somewhere that had "gone blue".

This turned out to be a reference, not to the political complexion of the town in question, but to the fact that some of its citizens had drawn attention to the need to be more dementia friendly by decking out part of the centre of the town in items of that colour.

Sad as it was to discover my mistake, this was more than compensated by the discovery that so much effort had been put into such a good cause locally.

It has been encouraging, recently, to read of significant scientific advances that may in due course enable the medics to defeat various forms of dementia.

But, for the time being at least, dementia is surely the dominant disease of our age.

As we live longer and longer, more and more of us find ourselves either in the grip of the disease itself or caring for somebody who is in its grip.

Having gone through a training course in order to become a "dementia friend" some years back, and having lived through some years of caring for a relative in this way, I am quite clear about both the colossal burden that dementia places upon our society and about the enormous amount of benefit that can be derived from quite simple improvements in the degree of awareness and sensitivity exhibited towards those who suffer from it.

So it is very good indeed to hear not only that the message of dementia friendliness is now being spread in this highly constructive way, but also that this has been accomplished by a series of practical steps to assist those whose lives are overshadowed by the need to care for someone in this condition.

This is the Big Society at its best.