Hi Steve
At the risk of boring people - yes, this poll is less valid than a YouGov poll or a properly conducted poll of people in the street. In a properly conducted poll, pollsters are given a cross section of people to go out and find who are representative of the desired population to be polled. In our case that could be, say, one for each 7 digit postcode in Forest Hill and Sydenham or three males and three females from each of a range of age bands who live within 2 miles of the Pools. Once they have got sufficient responses to meet each requirement they then reject any further responses in that group. Some groups can be easy to fill, others more difficult, but once all the results are in, they can be said to be representative of the population of interest within known statistical limits of error.