As you probably know, the three main parties in the UK are Labour, Conservative and the Liberal Democrats. They're standing pretty much everywhere, and Labour are currently in government. Discounting the nation-specific parties that only stand outside England (e.g. the Scottish National Party, Plaid Cymru and the Northern Irish parties), the best known minor parties are: the UK Independence Party (who want to leave the EU), the British National Party (who want to expel non-white people), and the Green Party. So a typical English constituency profile would have the three main parties, probably UKIP, and maybe one or two of the other well-known minor ones. Some places might also have an independent candidate.

Buckingham, on the other hand, looks like this:

• John Bercow – Originally Conservative, but not technically in any party as he's the Speaker of the House of Commons and is standing for re-election as such.
• Colin Dale – Monster Raving Loony Party
• Nigel Farage – UK Independence Party (until recently Farage was UKIP's leader and he is still their best-known face)
• David Hews – Christian Party
• Geoff Howard – Independent
• Debbie Martin – Independent
• Lynne Mozar – British National Party
• Patrick Phillips – Independent
• John Stevens – Buckinghamshire Campaign for Democracy, The
• Simon Strutt – Cut The Deficit Party
• Anthony Watts – Independent

No Labour, no Lib Dem. Technically no Conservative either, although that depends on how you look at it. UKIP's best-known guy. The BNP and the Christian Party (note to people in continental Europe – I know the last one won't seem odd at all to some of you, but we really don't do "Christian parties" in this country). Four independents, and two from such irrelevant parties that they might as well be independents. And, of course, the good old Monster Raving Loony Party – alas, their profile has declined since the 1990s since the death of their leader Screaming Lord Sutch, but they're still good for a laugh.

Initially, I thought Buckingham must be a haven of right-wing extremism where even the Labour party see a campaign as wasted money. But then I found out the real reason. Traditionally, the major parties don't challenge the Speaker. This is what's called a "constitutional convention". At this point I should probably explain that, to the surprise of every other country, most of the way our parliament works (including, for example, the idea of having a Prime Minister at all) is governed by convention rather than laws or written rules. Most of our conventions are pretty sensible, work well, and have the advantage over written rules that you can't hire a clever lawyer to find a loophole in them because they're enforced by the risk of losing other people's respect. But why this convention is felt to be necessary I have no idea. We're about to have a new parliament, so why not a new Speaker?

What this means is that the only people who are "allowed" to stand for election in the Speaker's constituency (wherever that may be) are the fringe parties. Consequently, they all see that constituency as giving them their best chance at winning – the only place where the Monster Raving Loonies have a hope is somewhere the sensible parties aren't contending.

This is what the Buckinghamshire Campaign for Democracy are annoyed about. If they don't like Bercow, their only real choice is UKIP – they have no opportunity to vote for Labour or the Lib Dems even if they want to.

UKIP, of course, chose to send their frontman to Buckingham for precisely this reason. And since Bercow's not technically a member of any party (although he's counted as a Conservative for the purpose of determining who has a majority), a large part of their campaign involves personal attacks on Bercow himself rather than criticism of the other parties' policies. Unpleasant, but not surprising for the guy who publicly insulted the EU president in the parliamentary chamber.

For most people this oddity won't be high on the list of things that need to change about our electoral system. The rest of the country is talking about the right of recall (allowing voters to sack their MPs between elections – amazingly, all of the big three have agreed on this), electing the House of Lords, and various forms of Proportional Representation. But for the people of Buckingham, the main issue is that this time around, they've drawn the democratic short straw and become the one part of the country out of 650 that doesn't get to vote for a party that can win. And all because of an unwritten convention.

Next time: the House of Lords – noblesse oblige.