To prove fraud, you need to be able to say that someone:
1) made a false representation
2) dishonestly
3) knowing that the representation was or might be untrue or misleading
4) with intent to make a gain for himself or another, to cause loss to another or to expose another to risk of loss.
Given that you are falsely representing your address (which is obviously dishonest), knowing that it is not truly where you are keeping the bike, and are intending to gain from it (in the form of lower premium), and that you are exposing the insurance company to more risk (maybe not by your definition, and maybe not sensibly, but by their risk-assessment), yes, you are committing fraud.
With regards to this voiding your policy, strictly speaking, yes this will. By not disclosing all material facts, you have taken out a policy without adhering to the principles of uberrima fides (utmost good faith), rendering the contract unenforceable (while allowing the insurance company to keep all your premiums).
In practical terms, however, if the claim was not for theft (or was for theft but not while at your home address), and your insurer is regulated by the Financial Ombudsman Service and you took it to them as a complaint in the event of a claim, it is possible that they would rule that you could pay the additional premium to bring your policy cover up to a point where you would have been covered anyway. However, given the large difference in premium cost, I think that this would be very unlikely.
In short, don't lie to your insurance company, or if you do, don't claim. At all. They employ people like me to find and detect fraud