These conditions tend to vary, presumably depending on how thievy your neighbourhood is.
My current policy (Brightside), which won't let me copy-and-paste the relevant boilerplate, says basically that they won't cover me against theft from home between 10pm and 7am unless the bike's locked in the garage; which actually seems reasonable to me.
I looked at the wording on my previous policy (Hastings) and found four separate endorsement clauses about garaging; they tell you in your policy schedule which endorsement applies to you (in my case it was clause 18 - the least unpleasant one I think):
14 Garaging warranty
Your insurer has accepted your insurance on condition that your motorcycle is kept overnight in a locked and secured garage. Failure to comply with this condition may mean your insurer will refuse to deal with any claim arising from your motorcycle being maliciously damaged, lost or stolen.
15 Garaging Warranty - (Increased Excess)
Your insurer has accepted your insurance on condition that your motorcycle is kept overnight in a locked and secured garage if your motorcycle is in the vicinity of your home address. Failure to comply with this condition will mean that the excess for each claim made under section 2 of your policy for theft or attempted theft will be increased to £500.
17 Garaging Warranty - (Excluding claims under Section 2)
Your insurer will not pay for any claim under section 2 for loss or damage by theft or attempted theft when the insured motorcycle is parked at the insured’s permanent place of residence and/or the declared garaging address, unless your motorcycle is kept in a properly constructed and locked garage.
18 Garaged Motorcycle Clause - (Increased Excess)
You have agreed that you will keep your motorcycle in a locked garage or building either at your home address or at the address declared to us when your motorcycle is not being used. If a theft or attempted theft of your motorcycle occurs within a 500 metre radius of your home address or the garaging address when the motorcycle is not in a locked garage or building, your insurer will double the compulsory excess.
One solution to the issue is of course simply not to declare that you have a garage at all, and then decide whether the resulting higher premium is worth paying for. I think it only made about £15 a year difference to me. Similarly, I certainly don't declare the use of my disk lock when out and about - it makes bugger all difference to the premium but I would no doubt get shafted if I did declare it, and the bike got nicked the one time I forgot to use the lock...