B&Q, two pieces of aluminium rod, cut to about 625mm each
Fit into an insulated holder one going up one down (piece of wood with holes drilled in it), with the ends separated in the "holder" by 50mm.
From the store earlier (use store finder on that site, plenty in london)
Some RG58 cable and a bnc connector (or one suitable for your scanner)
Hang aerial vertically in loft and away you go