Hi,

My understanding is that you can get married in the UK if you hold 5 years residence permit and your fiancee is on the tourist visa(mexicans do not visa for tourist purpose).This is the only case and only concern EU nationals.

http://www.workpermit.com/uk/fiance.htm

Otherwise she would have to apply for fiancee visa prior to her travel.

http://www.easyexpat.com/forums/ftopic_7614.htm

 

quick and simple

Right dude! 1stly u can get married in uk to ur mexian lady as long as both of you are there legally(u been eu national is legall).being mexican she does not need a visa to enter the uk.2ndly u are an EU NATIONAL with residence in spain.so she will get a spouse visa provinding the requirements are met. She will have to apply for the spouse visa outside the uk if she has entered for 6 months or less(req a visitors visa-allows u 6months stayONLY) and it will take you about 3-4 weeks. i no as my friend had to do his recently..but it also depends on the country where the application is being made...here is a short list of req: u may need to show when making ur application at the british embassy/consular.....it will greatly help her and the speed of your aplication if you are present with her.
www.britishembassytm.org.uk