What value have you put on your horse, how old is it, have you included LOU, what vet fee cover and excess do you have.
I would say £450 is on the highish side.
I pay about £35 pcm with NFU for an under-insured eventer (3K) with 5K vets fees
I also pay about £14 a month with KBIS for a retired horse, no value, 3K vets fees external/accident damage only.
I find KBIS very good for a taylor made package with lots of options for the cheaper horses, but quite expensive for comprehensive competition cover