In the UK under FPTP atleast, I can imagine there is also an effect or reverse gerrymandering or similar.<p>When it comes round to elections, generally the result of the majority of seats is already known, so they&#x27;re classified by parties into stronghold (ours), stronghold (theirs), marginal.<p>When your located within a Labour stronghold, your unlikely to see as much pro-Conservative media, as they are better off spending their time campaigning in marginals and defending their reputations in existing strongholds.<p>Surely, this effect simply compounds strongholds, making them even harder to change hands overtime, without a significant event to cause the public opinion to shift significantly (e.g. the Scottish independence referendum).<p>The only way to fix such a problem, would be to randomise the boundaries each election, but this would cause various extra complexities.