If I have understood the original question correctly I think you are both talking about two different services. If I am correct the initial question relates to the official Spanish Tax Office website whilst Mad Golfers response is referring to the UK based company Spanish Tax Forms. The UK based company offer a great service. They will calculate your tax liability and complete your 210 form. You will then be given the option to have you 210 form forwarded to you for you to pay your tax in to your bank, or for an additional £10 they will present your pament to the bank in Spain.
The other option is to pay your tax liabilty online via the official Spanish Tax Office website. On this website you can complete your 210 form and submit your payment online. Unfortunately it's not just that simple, to submit online you require an Electronic Key or PIN No. supplied by the tax office, for the life of me I cannot get this key. On the other hand you can complete your 210 form online print it out and present it to either your Spanish or UK bank for payment vis electronic transfer. The draw back here is that you need to know the bank account of the Spanish Tax Office to which you have to send your cash. Once again I am experiencing great difficulty in obtaining this bank account number. Once I get either the Electronic Key or the account number I think that the official online option is the preferred option as you will know your tax laibilty is correct and it's cheaper. I would appreciate any assistance in gaining either the Electronic Key or the bank account number of the Spanish Tax Office.