When I spoke to Mr Lewis last week, he made clear his belief that this is a widespread phenomenon on Facebook, where celebrity endorsements are often seen on adverts, even though the celebrities have not consented.
Martin Lewis said he found a fake version of a BBC article which was created and posted on Facebook
Facebook denies that, saying: "We do not allow adverts which are misleading or false on Facebook and have explained to Martin Lewis that he should report any adverts that infringe his rights, and they will be removed."
The company adds: "We are in direct contact with his team, offering to help and promptly investigating their requests, and only last week confirmed that several adverts and accounts that violated our advertising policies had been taken down."
That's not how Mr Lewis sees it.
Martin Lewis is the founder of MoneySavingExpert and often appears on TV to offer advice
He says that the company's response has been consistently ineffective, and that he is only taking legal action after repeated demands for more to be done.
Legally, there are several issues at stake here. One is the perennial issue of whether Facebook has legal responsibility for the content that appears under its banner - whether it is a publisher or a platform.
Another question concerns the legal jurisdiction in which Facebook operates.
Mark Lewis, the campaigner's solicitor, says: "Facebook is not above the law - it cannot hide outside the UK and think that it is untouchable."
Doubtless Martin Lewis, who was awarded an OBE for his remarkably effective campaigning, calculates that the publicity around his case will alert some Facebook users to the fact that these false adverts are rife on the social network.
It's been a difficult few months for Facebook. Now Martin Lewis is about to give them another big headache.