You can visit http://www.lewisbaston.com/the-2015-election-under-3-4-member-single-transferable-vote/ to see what the result of the 2015 General Election might have been if STV had been used and the voting pattern had been similar to the pattern in the actual FPTP election.
We are not saying this is exactly what would have happened but it does show what could happen. Although the author, Lewis Baston, had to make several assumptions to produce this projection so accuracy cannot be guaranteed, he is a very experienced political analyst.
If you support one of the two major parties in one of its strongholds, you may be concerned to think your party would probably lose seats in your region, but look at the regions where your party is less strong and see how it could win more seats there.
More Labour MPs in the south and rural areas and more Conservative MPs in the north and inner city areas would help each party to understand better the problems of those areas and reduce the north/south and town/country divides.