Intracomunitary EU number

I am a self employed translator based in the UK. One of my clients is based in Spain and they are asking me for my "intracomunitary number". I am not sure exactly what that is in the UK (where I pay my taxes). All I have is my Unique Tax Number, and apparently that is not the number. I had phone HMRC but they are not sure what it is. It is all linked with Intrastat rules. Basically the Spanish company needs a number (normally GB plus a 9 or 12 digits number) that identifies me as a EU company. They also told me that once you get that number you need to be register as an intracomunitary operator.

All I can think of is that this would be the VAT number in the UK with the GB at the start. But I see to charge VAT you need to exceed 70,000GBP per year, a figure that I do not reach. I wouldn´t like to register for VAT and then find out that is not the actual number.

Does anyone know how can I get round this situation, please? Will I need to register for VAT in the UK then or can I be included in the intracomunitary operators system without this number?

Many thanks for your help.

Kind regards

Julio