Proving ID for UK solicitor

[Trooperman]

As in the title, really!

A relative's house in the UK is being sold and I have a financial interest in that house. The UK solicitor has to comply with money laundering regulations and is asking me to get a (Spanish) lawyer or bank manager to verify who I am by way of a written statement to that effect.

Is this not a sledgehammer/nut means of doing it?
Has this happened to anyone else?...and if so what means are there of complying with UK regulations?

[Parilla]

I had a similar situation recently, and the UK solicitor accepted a copy of my passport certified by my Spanish lawyer as a "true copy", with the certification text (also confirming my Spanish address), in both Spanish and English.

Parilla