Your link leads to a butterfly (not a swallowtail) which we don''t get here...

We do have a Swallowtail butterfly, they're Britain's largest butterfly, seen usually in Suffolk, Cambridgeshire and the Norfolk Broads, but it doesn't look as you describe. It has some iridiscent blue, but only in dots along the bottom of both wings and is primarily yellow, with two distinctive projections at the bottom (the tails) see link below

http://www.ukbutterflies.co.uk/species.php?species=machaon

A rare migrant we might see here (usually to the east of the UK and along the south coast) with some iridiscent blue, again in dots along the bottoms of the wings, otherwise primarily black with a yellow trim is the Camberwell Beauty. I don't know of any butterfly we get here which has that colour in the centre and running downwards.

Maybe a Purple Emperor - the male has quite bright blue markings on the lower wings, sometimes also on the upper wings, otherwise dark brown with white spots, perhaps it was one of those (distribution central southern England and the midlands).

Thank you Bamboo it was around 3.0clock it came so have now been watching for it again .
The wings were long not rounded like a normal butterfly it was like black velvet , when it landed on the fan palm I could see a bit of fluorescent blue in the centre there were no other markings on it. I think I ll have to draw it wish I had my camera handy but by the time I went back out with my camera it had gone.

We sometimes get a very large iridescent turquoise dragonfly, could it have been that?

Defiantly not a dragon fly Owdboggy thank you it was quite big when I find my pencils and colouring pens I shall draw it.