Trying to get others to quote including instruments is not that 'simples' as many won't quote at all.
I will second this, from the last time I was shopping around for house insurance.
I reckon the melodeons are the only things I have which are over the £1500/ £2000 'Single Article' limits on Contents and Personal Belongings cover - as such I have only one covered, for £2K, which is now likely underinsured with the fact of increases in price of other boxes which have now passed the £1500 limit. Similarly, it has bumped up the overall limit I had previously set for any Personal Possessions which may be out of the house at any one time (now including almost invariably digital camera and recorder). That one box at £2K cost me an additional £20.35 - which has not risen for the last 2 years BUT this may not be a true reflection of costs ie the cost of both Contents and Personal Belongings Sections each increased between 15 - 20% last year - so, have one expensive item, and they may suspect that you have several more at around the Single Article limit price...
Anyway, to get back to Scallyanglo's point, having 'come of age' I tried various people like SAGA and, yes, they didn't expect you to have any expensive items! (perhaps music-making is deemed akin to some kind of dangerous sport, not expected to be indulged in once over a certain age...!).
Boxes tend to fall into 2 categories - those which are almost always over £1500 nowadays, and refurbed old Hohners, etc., which rarely fetch more than £600 (Preciosas). So, I may look to leave the old ones on the normal Household Cover, and get something more specialised, such as New Moon, to quote for the others.
Diane
