Hi Greg, since you're in London, its unlikely there are no Theravāda centres within easy reach. There is always the Buddhist Society in Victoria, which holds meditation classes.
Theravāda tends to rely on the Pali Canon (not the Pali Cannon — that's what we use to shoot down people who hold wrong views
) If you read only certain parts of the Canon, then it is hard to avoid the teachings on rebirth, and realms of existence, but the meditation teachings like the Satipatthāna Sutta don't even mention other realms of existence.
To say that the Buddha was just an ordinary man, like you or me, is to seriously over-estimate one's own abilities. The human mind has a vast range of abilities, and some are more gifted in certain areas than you or I will ever be, though they may be severely retarded in other ways. Can you read the thoughts of others? If you try to explain something to someone, do you know beforehand whether they just need a slight hint, a brief explanation, or a comprehensive exposition of the topic?
The full range of mental prowess in human beings is even greater than the range of physical prowess. I probably couldn't run 100 metres in 19.19 seconds, let alone 200 metres.
It takes both inherent ability, and prolonged training to gain deep concentration and insight. The Buddha's insight was extraordinary and immeasurable. Many monks who live an austere life and practise in remote forests for the whole life still fail to gain the highest goal of Buddhism, and even those rare individuals who do attain Arahantship, lack the special powers of the Buddha.