Can't see why your solicitors told you this on 8th March. Look on lots of posts here and you will see the law changed at the beginning of this year. You have to apply for your own NIE now but you can get someone to go with you to smooth the way in terms of translation etc.
You apply at a police station or local town hall (with a police station in it). If you go to the office which issues the numbers, you may be lucky and get them the same day (bit of hassle but smiling sweetly seems to work).
If you go anywhere else it can take about 4 weeks to get the certificates with the NIE numbers. These are all free of charge.
You can apply through the Spanish consulates in UK but some people have mentioned they tend to get lost or take absolutely ages to come through. I believe you also have to pay.
Have a look at the NIE threads and all will be revealed (in between the thread drifts of attaching signatures, avatars,pretty pictures of peoples swimming pools and favourite restaurants).