Is a Towbar a modification regarding Insurance?

I have asked this question to 'The Expert' but no answer to date and insurance is due in 2 weeks!

I have read that a caravanner has been charged an extra £80 on his insurance when he declared that a towbar had been fitted as it was classed as a 'modification'?

I have been towing for over 43 years and even when declaring a towbar, never asked to pay extra nor had been told that it is a modification.

Has anyone else heard about this as it was also stated that your insurance would be void if not declared?