Help getting TIE.

From your question I'm assuming that you are already living here in Spain? 

If so then using a Gestor is probably the best option. 

If you are still living in the UK with a UK passport then the first thing you need to do is apply for a non lucrative visa to be able to live in Spain. You will need to meet the income and healthcare requirements. 

Steve 

Previous posts suggest OP may be resident, presumably with a green residencia?

If so a switch to a TIE is an administrative process which should not involve any questions about finances.

Many Gestors around who will perform the service for around €60-100

I had a quick look through previous posts and I couldn't see anything where O/P stated he had residency. (might have missed the obvious though)

Perhaps O/P could state whether he has a residency certificate, or just a NIE number?

Have residency.

If you already have a green EU registration card you can apply online for an appointment in Alicante. It will take two visits which you would have to do even with a gestor or agent as you have to provide fingerprints at the first interview and give your fingerprints at the second interview.

The new TIE will be issued at the second appointment. Just a nuisance getting the appointment at the moment and you have to keep trying.

You need an EX23 form completed and a Tasa 790-012 to pay the tax of 12 euro (either through online banking or at an ATM). 

Plenty of sites online but this is the one for making the appointment#

https://sede.administracionespublicas.gob.es/pagina/index/directorio/icpplus

The option you now require is National Police - Fingerprint card taking Long term card renewal

Then follow the instructions given for the EX23 to change the green card to a TIE

It tells you what documentation to take with you including the bank receipt for the payment.