Problem is that the Met Office is trying to forecast a future event which, in the UK, isn't completely forecastable. We're a small island, off the coast of a large land mass, with a huge ocean with warm most air to the West and a source of very cold dry air to the North. Add to this the variability of the jetsream moving around and it all becomes very complex very quickly. If you want an accurate forecats, move to Nevada.
Another problem is the decrease in forecasts based on actual data capture from met station/observation points/sounding/buoys/ships, etc. So much of it is now computer modelled. So, we have computer models doing predictions based on computer generated data. Take out the human experience factor and it's no surprise that the forecasts aren't up to much.
I think the forecasts would improve if they opened the blinds at the met Office in Exeter and let the forecasters look out the window.