First because now you have to be in person at the police station yourself (lawyers with power of attorneys are not able anymore to request the NIE without the presence of their client), second because you can request the NIE at your local Spanish consulate (there is a Spanish consulate in every major British city).
Last but not least any professional Spanish lawyer will include the NIE request in the standard conveyancing package free of charge…
A new law has now rendered the POA almost useless to apply for a NIE number except in some municipalities.
Now foreignerns can either:
1.- have to file for them they themselves (a POA will be rejected by most National Police Stations and it is not legal after the new law)
2.- or else apply for them at a consulate in their home country taking months
No lawyer should be charging to obtain a NIE number after the enactment of this law IMHO.
Anyways, in a near future the NIE number will be abolished for EU citizens it seems.