A tax on chewing gum is needed to help meet the £150m annual cost of cleaning it off streets, council representatives from across the UK are expected to say. A first national "gum summit" in London will call for a penny-a-packet tax. The Liberal Democrats have also called for anti-litter messages on packs, and the development of biodegradable gum. Gum maker Wrigley's says £5m research on that has been unsuccessful. Cardiff, Westminster, Edinburgh and Belfast representatives are due at the summit. Lib Dem London Assembly member and environment spokesman Mike Tuffrey said: "Chewing gum that is irresponsibly spat on to...