A useful site provided by the Junta de Andalucía and the national statistics institute gives some numbers for Mojácar. Accurate or not (the INE relies on the padrón for its information), these are the numbers used by the authorities.
We see that there are more foreigners than Spaniards in Mojácar (although, curiously, there are none working in the Town Hall, neither is there any apparent acknowledgement of their presence).
A few points:
Not all foreigners are British, of course, but also not all Spaniards are Mojaquero. The largest foreign group is British.
Population: 6,825, of which foreigners: 3,486 (54.8% of the population).
Health Centres: none (there are, in fact, two).
Cars: 4,251 (this can't be right, as this is the number of cars registered by Tráfico. Many 'guest' cars are here, probably most of which are semi-permanent, and also, Tráfico won't de-register an old car without a struggle.