De-icer spray is the quick fix for a frozen windscreen. You spray the alcohol-based fluid onto the glass and it melts ice on contact, clearing your view in a minute or two without scraping or waiting for the engine to warm up. A 500ml bottle costs only a few pounds, lives easily in a car door pocket, and is the fastest way to get moving on a frosty UK morning. What it does not do is help once you are actually stuck: it clears glass, not the snow packed around your wheels.
A folding shovel is the answer to being stranded rather than just frosted over. It collapses down to fit in a boot or rucksack and opens into a proper digging tool, letting you clear snow from around the tyres, dig out a driveway, or spread grit and traction under a spinning wheel. Many include a serrated edge or a pick for breaking compacted ice and frozen ground. It costs more than de-icer, usually around fifteen to thirty pounds, and it is slower to use, but it deals with the situations that a spray bottle simply cannot touch. The two cover completely different winter-driving problems.