First heard of them about 18 months ago Christian, so they have deffinatly been around that long and the bottom of the site quotes

"dayinsure.com is underwritten by Norwich Union Insurance, a member of the Aviva group.
Norwich Union Insurance Limited. Registered in England Number 99122. Registered Office 8 Surrey Street, Norwich, NR1 3NG.
Authorised and Regulated by the Financial Services Authority."

The web name is registered via SCHLUND+PARTNER AG and is owned and operated by Vince Powell of DCML in Stockport Manchester and hosted by 1and 1.

Trace DCML back and they have a portfolio of vehicle related products
http://www.dcmnet.com/public/index.aspx

Make your own mind up if its fly by night or not though