commencement of liquidation. It has also been suggested, relying upon obiter dictum comments by Lord Macnaghten in Government Stocks and Securities Investments Co Ltd v Manila Rly Co that a charge should also crystallise upon the company ceasing to trade as a going concern. However, this view is not yet supported by judicial authority. In certain countries, notably Australia and New Zealand, it was for a time very common to include "automatic crystallisation" provisions which would provide that the floating charge would crystallise upon an event of default automatically and without action from the chargee. Automatic crystallisation provisions have been upheld in New Zealand but there are judicial comments suggesting they may not be recognised as effective in Canada. In the United Kingdom there is some inferential support for the validity of automatic crystallisation provisions, but they have never been subject to full judicial consideration. Priority The main purpose of any security is to enable the secured creditor to have priority of claim to the bankrupt party's assets in the event of an insolvency. However, because of the nature of floating charge, the priority of floating charge holder's claims normally rank behind: holders of fixed security (such as a mortgage or fixed charge); and preferential creditors, who are given priority by statute. The floating charge cannot normally be enforced until it has crystallised (and thus, effectively, become a fixed charge) and so most statutes provide that the priority of a fixed charge that was created as a floating charge is treated as a floating charge. Because of the differences in priority of fixed charges and floating charges, security documents came to be drafted to contain as many charges expressed to be fixed charges as possible, and leave as little as possible covered by the floating charge, where it would have secondary priority to the claims of the preferential creditors. A number of judicial decisions gave conflicting interpretations over the characteristics that were definitive of a fixed charge, particularly with reference to charges over book debts (and a fixed charge that did not contain those characteristics would be "recharacterised" as a floating charge). The position was definitively resolved in NatWest v Spectrum Plus Limited when the House of Lords confirmed that a charge over book debts could be a fixed charge, provided that the secured creditor exhibited the necessary degree of control over the proceeds of the book debts. This would