Spain is feared to have spied on Scottish MPs over their work on Catalonia, the Commons has heard.
Plaid Cymru's Hywel Williams (Arfon) said it appeared that members of his party, the Conservatives and the SNP were subject to covert surveillance by agents of the Spanish government in respect of their activities as members of the All-Party Parliamentary Group (APPG) on Catalonia.
He raised a point of order to air his concerns about "spying by a supposedly friendly country".
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A push for Catalan independence in 2017 by officials in the region failed, sparking a major political crisis.
Mr Williams told MPs: "From documents lodged in a Barcelona tribunal by the Spanish government, it appears that members of this House - from the Conservative Party, the SNP and
Plaid Cymru - have been subject to covert surveillance by agents of that government in respect of their activities as members of the APPG on Catalonia.
"Reference is made to meetings of the APPG, including one addressed by Josep Costa, the deputy speaker of the Catalan parliament, who on that occasion also met the chairman of Ways and Means (Sir Lindsay Hoyle).
"The APPG meeting was a public event and there was no need for participants, even those from the Spanish government, to hide their identities. This matter has some way to go.
"Reference is also made to Elin Jones, AM for Llywydd at the Welsh Assembly, to the First Minister of Scotland (Nicola Sturgeon) and many others - and indeed including our own Speaker (John Bercow), who when responding to a point of order on February 13 in respect of the imprisonment of Carme Forcadell, the speaker of the Catalan parliament, gave me a very favourable response.
"That reference in the document is summed up by the headline this morning 'El Speaker no es imparcial' - clearly that was the Spanish government's opinion of our Speaker."
He asked Deputy Speaker Dame Eleanor Laing to confirm that the principles of openness and free debate are the "bedrock of the workings" of the Commons and its APPGs, adding: "And that spying by a supposedly friendly country, for that is what this is, has no place here."
Dame Eleanor said it was a "very serious" point of order and confirmed that the principles Mr Williams raised "must be respected at all times".
She added: "I do take very seriously the points (Mr Williams) has made and I'd suggest he ought to make his points in writing to (John Bercow) so Mr Speaker can give this matter his proper consideration, not just a momentary consideration here in the chamber."