I had mine insured with sainsburys, called them to mention the mods and they didnt increase the premium I obtained over the Internet,
As far as I can see if they list the dc5, take your money and send a cert of insurance you are insured, if they don't cover imports they shouldn't list them and take money!
I think though various other members have discussed the validity of insurance with sainsburys.
It is an anomaly for sure, incidentally I moved my ins off the teg to a type s civic and they wanted an extra £300---- that's another story though
I'm back with sky now