Lets assume for 2 mintuies that speed isn't the factor to accidents and that the UK government then remove the speed limit on all motorways. All the money they bring in for catching people breaking THE LAW is then lost. Do you want your taxes increased further? I already work 2 days per week to earn enough to pay the government for the privalege of living in the UK, I'd like to keep the other three for me to earn to choose where and how I live.
People then drive faster, on roads that aren't designed for these increased speed, with worsening road surfaces and safety barriers that can't contain the vehicles travelling at higher speeds. We certainly dont have the money to change any of these three new problems.
We then have some fantastic donation from a random billionaire, you lot will only complain that the Gov then closes all the roads with repair works and improvements.
Assuming even that they increase the limits from 60 to 100, on a 20 mile journey you'd only save 8 minutes. On longer jounies it does make more sense, but how often have you over taken a set of slow moving cars, only to ge to the next corner and find someone willing to do 60 in lane 3 and you have to slow down again or break the law and undertake them?
At the end of the day, the law is the law, and if you dont like it, group together, get yourselves voted into the local council and start making a fuss about it. You only need ~1000 people in an urban area to vote for you to get elected. The uk voting population is only 44m and only ~60% actually vote, so 26.4m, and you only need ~35% to get in power, so setup a Facebook page and find yourselves 9.24m friends.