How to move here

You are from UK with a British passport. You cannot apply for residency from Spain as you need to apply for a visa from a Spanish consulate in UK. There is a load of information on this site on how to do this included in the tips and how to section.

Basically, you can apply for a visa that suits your needs.

The Non Lucrative Visa which allows you to move if you meet the requirements but it is for those who are retiring here as you cannot work under this visa.. You need to show and income of €28.800 or more per year and €7,200 for anyone moving with you.

You need to have medical insurance that covers you on the same basis as the Spanish NHS unless you are over retirement age in UK in which case you get an S1 to transfer your healthcare across.

You also need a medical certificate and a criminal background check officially translated to Spaniah.

You then apply for the visa in UK which allows you to come to Spain to apply for residency for one year. You then update the visa in Spain after 1 year and 4 years showing you meet the same requirements as originally. After 5 years you become a permanent resident and no longer have to provide proof. During the first 5 years, you cannot leave Spain for longer than 6 months at any one time or 10 months in total in the 5 years.

There are other visas such as a work visa but you still need to show the same requirements and have a certified offer of work with a contract from a Spanish employer which accompanies your visa application.

Just look at all the advice on visa on here but bear in mind you will require 28,800 euro a year income and medical cover.

Do not overstay your 90 days in Spain or you will not be allowed to apply for a visa.

A correction: you have not moved here, you are a visitor for up to 90 days and cannot stay longer.

You will need a visa to move and that must be applied for in UK before coming to Spain.

There is nothing you can do when here and must leave after your 90 days, if you get labelled as an overstayer you can be barred from reentering Spain and it will almost certainly stymie any chance you may have of subsequently getting a visa.

Sorry but that's the reality of it since Brexit.

As a non EU/EEA Citizen you are right in that you cannot stay beyond 90 days out of 180 days (see links below).  If you stay in Spain for more than 90 days within a 180-day period, you will violate the 90/180-day rule and face penalties. These penalties can include paying a fine, leaving the country, and being banned from entering the Schengen Area for a specified period. The following links explain the various types of visas that you may be eligible to apply for through one of three Spanish Consulates in the UK (London  Manchester and Edinburgh).  Any visa application must be made by you and in the UK.

https://www.exteriores.gob.es/Consulados/Manchester/en/ServiciosConsulares/Paginas/inicio.aspx

https://www.exteriores.gob.es/Consulados/Manchester/en/ServiciosConsulares/Paginas/Consular/Visado-de-residencia-no-lucrativa.aspx

https://www.immigrationspain.es/en/spanish-residency-for-uk-citizens/

https://www.gov.uk/guidance/living-in-spain

https://www.schengenvisainfo.com/spain/how-long-can-i-stay-in-spain/uk/#:~:text=If%20you%20stay%20in%20Spain,Area%20for%20a%20specified%20period.

https://www.visa-calculator.com/

Thank you for your response. I am going to do more research on what you’ve said. 
A few people I’ve spoken to before coming here did say that it was easier to apply from Spain while I’m already here. What would you say is easier? 

Someone else also mentioned that here in Gandia the police station deal with most of it and that I would just need to go there with my documents- passport as that’s all I have. 

I am here as an aupair and the mum is a manager of a hotel so I could possibly get a work contract. I also plan on doing an online  teaching course so I could earn more money. Would you say getting a work contract is the easiest and quickest option?

Ideally I would like to stay here for a year. This is my first week here. Do you suggest I go back and apply and then come back to Spain once I have my visa?
Imara  

You say you are from England with a UK passport.and therefore you cannot apply for residency when in Spain. That is only available to EU citizens holding a EU passport.

Do not, repeat not, exceed your 90 days here as you will be barred from applying for a visa and may even be barred from entering Spain for up to 2 years. 

Work permit, will you get a guaranteed contract paying the amount needed? You would not need private medical care as you would pay social security. But you cannot apply, even for a work visa, whilst in Spain.You must have an official offer of work with a contract and apply at a Spanish consulate in UK for the work visa which would allow you to come to Spain to apply for residency.

You are being wrongly advised. Listen to what you're being told here not to whatever I'll informed nonsense  you're hearing which fits what you'd like to believe or would hope for.

As a UK passport holder your ONLY option is as outlined, applying for a visa in UK.

There is no way to do anything whilst here in Spain.

Ahh yes that makes sense. Would the British Embassy in Madrid maintains and develops relations between the UK and Spain, be of help? 

No, they do not get involved in individual residency applications. Spanish consulate in UK (Manchester, London and Edinburgh) will be the only ones dealing with the application. Once you have a visa agreed and put in your passport, you have 3 months and 15 days to travel to Spain to apply for residency in the province you are going to be living in.

The Police in Gandia deal with most of it? The visa application? Who is telling you this rubbish? 

If you are in Spain as a UK tourist, with the clock running down on your 90 days, you should not be working as an au pair as this is illegal.

 If you want to live in Spain, go back to the UK and apply for a visa.