megasue, I don't think you understand me... I'm not trying to put you off, just tell you how it is
In order to get a job as a 'proper' reception teacher (bearing in mind that the starting school age over here is 3 years old, so reception is actually infants) you would have to be fully qualified with SPANISH qualifications, so this would mean sitting some sort of bridging qualification to legalise your UK ones. You would have to do this at La Laguna University and I am unsure of the actual length of the course, but it would be at least a year.
You would have to be FLUENT in spanish in order to a) take the course and b) teach. If you are not fluent now, then you are looking at at least 5 years of hard study to bring yourself up to the required levels.
Once you have done all this, the actual application procedure for becoming a teacher is fantastically complicated. I personally think it is madness, however this is how it is done :
You apply to be a teacher and you are put on a 'list' and allocated a number (bear in mind that there are already lots of teachers on this list already, so you would be in for a wait).
Jobs in schools are allocated to the teachers on this list in order of number. You have a higher number based on how many 'points' you have. Points are allocated for each year you work in the SPANISH education system, how qualified you are (with Spanish qualifications, extra courses etc.) and whether or not you have passed you oppositions (this is another more complicated thing to explain, so I will leave it to another post!).
'IF' there are places after all the other teachers have got one, and you are lucky enough to be asked to teach, you can be sent ANYWHERE. You could be allocated to a school on El Hierro, La Gomera or Gran Canaria... and get this, If you REFUSE to go, you go back to the bottom of the list.
To give you an example of the waiting and battling involved, the English teacher that I assist in my school is from Venezuela, but came to Tenerife when she was 6, so did her University qualifications here etc etc. SHE took all her qualifications in Tenerife and is Spanish (so therefore fluent

).
She is now about 45 years old and has been teaching for about 15 years. Prior to that, she was a qualified teacher, on the waiting list, but had to take a job in a hotel while she was waiting for 10 years-ish.
When she finally got a placement, she spent a couple of years in La Gomera and some time in Gran Canaria, where she had to comute back to Tenerife every weekend in order to see her family.
She is now at my school for the next year at least, but because she has not yet completed her oppositions, her place is still tentative after that period and she 'could' be moved anywhere! She lives in La Oratava and commutes to the wet coast every day for the job. The journey is 1.5 hours by car each day.
Once again, I am not trying to destroy your dream, but if you are being realistic, without having at least competent Spanish that you can build on now, you don't have a chance of getting a proper teachers' school job.
You WOULD have a chance as a teaching assistant though, although as I said, the number of positions are limited and new ones only open up if a new school applies to join the project, or a current assistant leaves. You may think that 18 hours a week is not a lot, but the pay is very good and works out only just lower that a 40hr bar or chef job. Also, you can supplement your income by doing private lessons, as a lot of the assistants do.
If you want to apply for that, you would need to be resident first, however I could give you the address to send your CV to. It would also be advantageous to have your TEFL qualification, though not essential (it depends on experience more than anything) and you DON'T have to know any Spanish to apply.
The other alternative, as I have mentioned earlier, is to either contact the private English schools such as Britannia, Wingate or Yeoward, or set up doing private lessons yourself.
Those are really your only options.
I hope this is of help!