Tory MP David Cameron explains why sitting on a select committee has been the most rewarding part of his first year as an MP

Even the most devoted parliamentarian cannot help pondering what I call the "Brandreth equation". This is the relationship between the time devoted to doing something and the recognition for your hard work.

In his much-underrated diary as MP for the city of Chester, Breaking the Code, Gyles Brandreth recalled being taken to one side by Brian Mawhinney MP (then Conservative party chairman) and told: "Met your chairman the other day. Says you're never in the constituency."

A fuming Mr Brandreth then reeled off his constituency diary for that week: architects' conference at the town hall; training into jobs launch; visit to the regimental museum; Samaritan's charity walk; opening the Save the Family offices; and so on. Yet as he did so he realised the problem: no one in the local party had a clue what he was up to.

Sitting on the home affairs select committee would probably get a low score on the Brand-o-meter, but it is far and away the most interesting and satisfying thing I have done in my first year as an MP.

Most of the last 12 months have been devoted to our investigation into drugs. We have received more than 200 written submissions and spent some 50 hours in evidence and deliberative sessions. We have heard from 45 witnesses, including experts, lobby groups, professors, drug addicts and parents of addicts who are in prison or who have died.

We have quizzed ministers and medical experts, police officers and policy wonks.

There have certainly been high points. We coaxed police commander Brian Paddick into one of his first indiscretions; contradicting the official police line by saying that he thought the drugs laws needed changing. He's hardly been out of the news ever since.

I managed to prompt a medical expert into summing up the dangers of ecstasy by revealing that it is not the drug that kills you, but the dancing. This exchange led to my maiden appearance on Yesterday in Parliament - and appalled many of my more elderly relatives.

The testimonies from families with children who had died from drug abuse were intensely moving. In some cases they wanted even hard drugs legalised so that addicts would not use the black market, deal with criminal gangs and inject impure and often lethal substances.

The low point was a 10-minute discussion on whether we should use the phrase "black market" at all. Parliamentary protocol prevents me from revealing the PC-obsessed MP who started this nonsense.

The same protocol also prevents me from telling you what is in the report, which will be published next Wednesday. (Although I note that some unscrupulous member has already leaked some of the contents to several broadsheet and tabloid newspapers.)

But do these worthy committees really achieve anything?

My answer is a firm "yes".

The evidence is taken systematically and in detail. Ministers are questioned forensically. Party allegiances are, by and large, put to one side. Above all, minds are opened - and then changed. Several members - including this one - admitted frankly to changing their minds during the course of the inquiry, often more than once.

In the process of drafting the report real cross-party working takes place. If one member has a concern about a particular recommendation, others join in and try and redraft it in a way that can keep as many members on board as possible. The aim is to produce a report that all can sign, support and promote.

But will anything actually happen?

The government has to respond inside eight weeks, stating which recommendations they accept and reject. A debate on the floor of the house is likely to follow.

"Big deal", you might think, but shaping the wider national debate is perhaps the most important thing a select committee can do.

Drugs policy has been a no-go area for most politicians, with a few notable - and brave - exceptions.

Taking a "tough" line, calling for a "war on drugs" and stiffer penalties has been the stock in trade of politicians of both major parties.

Proposals to liberalise the law lead to accusations of being "soft on drugs" and cost votes.

A cross-party committee - so the theory goes - can put aside such concerns and think the unthinkable.

The simple, bold answers are superficially attractive.

Whether it is the authoritarian "introduce life sentences for all pushers and zero tolerance on street users" or the libertarian "legalise all drugs, destroy the black market and treat, rather than punish, those who abuse drugs", both offer seemingly easy solutions to a problem that haunts all western governments.

I am an instinctive libertarian who abhors state prohibitions and tends to be sceptical of most government action, whether targeted against drug use or anything else. And on the drugs issue, libertarians and sceptics can have a field day. About the only thing all our witnesses agreed on was that the government's strategy was a failure and prohibition over many decades had not worked.

But politics has to be about the practical not just the theoretical.

Legalisers have to accept that decriminalisation will lead to greater availability, and therefore increased use. They can counter that increased use may not lead to increased harm, as legal, regulated markets replace illegal, unregulated ones. But certainties swiftly lapse into probabilities, even possibilities.

Authoritarians have to accept that the world has changed and hounding hundreds of thousands - indeed millions - of young people with harsh criminal penalties is no longer practical or desirable.

Witness the fate of Ann Widdecombe's plan for cracking down on cannabis: it didn't make it through the Conservative conference. And to misquote Frank Sinatra, if you can't make it there, you can't make it anywhere.

Without the bold and the simple, you are left with rebalancing the approach we take as a country to reduce the harm drugs do, to cut the crime they lead to and to ensure that the law actually makes sense.

Thin gruel? I think not.

If what we say, and what is subsequently done, ensures that a few more ravers understand that ecstasy use can lead to dehydration and death, or helps one heroin user to access treatment before overdosing, it will have been worth it.

And, who knows, if a better understanding of the drugs epidemic in this country means that addicts are treated quickly, rather than left to burgle, rob and mug for their drug money, maybe the broad swathe of public opinion will be with us as well.

· David Cameron is the Conservative MP for Witney and sits on the home affairs select committee.