The UK has no constitution, or as every first year law student learns, it has no constitution written down in one grand document. Rather it has laws, conventions, practices, activities scattered all over the place that constitutional lawyers then gather together and describe as the UK constitution. This is unusual, to put it mildly.

Sure, there is a reason for it. Britain has never suffered the sort of defeat in war or other upheaval that produces a new constitution, nor has it ever had to free itself of colonial rule – it was always the coloniser. When it did have a revolution in the 17th century, constitutions were not yet in fashion. But most countries now have a written document that captures what a place is about and sets out how power is dispersed. You don't have to be a democracy to have a constitution – look at Belarus and China. Nor do you need to be a republic – both Belgium and Sweden have monarchs for example.

Not having a constitution is problematic as well as peculiar. The country reels from crisis to crisis – failing banks, economic collapse, controversial wars, MPs' expenses – without having any clear idea of what it stands for, what principles and values matter to it, and therefore how best to tackle the various problems that it confronts. Some of the gaping holes in our thoughts are specifically constitutional: what should we do about the European Union? About immigrants? Does the House of Lords make sense? Do we really want the Prince of Wales to be our king? Who are we anyway?

Many experts have tried to draft a constitution, going after this holy grail for centuries, meeting in their ancient college rooms, talking to themselves, reporting to their peers, dividing opinions and invariably cancelling each other out. Where they have managed to agree, usually on something pretty small, they have come up against various insuperable obstacles. Meanwhile, Europe takes more and more from Westminster, while Scotland threatens to grab its bit of land and wander into independence. Some parts of England agitate for their own regional assemblies. Where does all this leave Wales? Not to mention Northern Ireland.

Many feel that the status quo is no longer an option, that on the 800th anniversary of Magna Carta in 2015, we can – and should – do better than a bunch of medieval barons in Runnymede in June 1215.

If the UK needs a formal constitution, the main question is not what it should comprise, but who should write it? The answer is: the general public. In a unique project, LSE's Institute of Public Affairs (IPA) in conjunction with its law department, public policy group and democratic audit, are pioneering the crowdsourcing of a new UK constitution.

We are asking the public to participate in, offer advice on and eventually to draft a UK constitution. A website, constitutionuk.com, will provide a forum for debating suggested values for its content, such as: equality of esteem, the celebration of respect for diversity, the protection of freedoms, subsidiarity and the guarantee of human security. But of course the process might produce other values, for example protection of the family, respect for community or a space for God. We expect our values to drill down into actual principles which will guide the drafting of our constitution in a more specific way.

A complementary Twitter feed at @ConstitutionUK, a Facebook page and a YouTube site broaden the project's reach.

The public launch today will firm up what the principles and values should be for the proposed new constitution. Over the course of the next six months, live-streamed videos on the website will foster discussion and debate over the content, with a draft document further honed at a constitutional carnival in spring 2014.

The people's constitution will be finalised on 22 June 2015, on the anniversary of the eve of the moment King John put his seal to Magna Carta.

Come to ConstitutionUK and join the debate – and in the thread below, tell us what you think are the worst and best features enshrined in the existing British constitution that you would like to abolish or retain?