Torrevieja is the city in the Alicante province with the greatest number of EU foreign citizens that have registered to vote in the next municipal and autonomic elections on the 27 of May. Out of the 6,538 EU citizens there are 3,767 (almost 58%) British Nationals registered. You can bet your bottom dollar that the political parties in Torrevieja are geared up to impressing these people with their policies.
Following Torrevieja is Jávea with 4,084, Calpe with 3,007, Teulada with 2,987, San Fulgencio with 2,930, Orihuela with 2,925, Rojales with 2,724, Benidorm with 2,375, L´Alfàs of the Pi with 2,340, Dénia with 2,206, Alicante with 2,093 and Elche with 1,725.
I don't have any figures for Bigastro. In 2005 there were 6,450 inhabitants which was an increase of 849 on the previous year (by far he largest increase the town has seen since 1950). I imagine the percentage of UK citizens though was quite small and still is.