Well David Davis's decision has put a no of individuals in the main political parties at sixes and sevens. Esp now that Kelvin Mackenzie has decided to stand should Labour not field a candidate. This puts those Labour Party activists who are for or against and who want to be involved at a quandary. For those who are against the extension it would mean not being involved because that would mean supporting David Davies. For those Labour activists who are for the extension, I doubt many of them would be happy at the thought of helping Kelvin Mackenzie campaign for any form of elected office.
Equally for the Conservatives it is difficult. Some of them are for the extension it means they feel they have to support their candidate in a by-election on a platform against the extension, the alternative being a desire to see a Conservative fail to win a Parliamentary seat. For those who are against the extension it means dealing with potential splits within the Conservative Party that they don't want to see exposed just yet!