WHEN I moved from the Home Office to the Foreign Office five years ago, I visited a primary school in Blackburn and was asked to spell out the difference.

As the youngsters' eyes glazed over with the tedium of my explanation, I realised I'd failed in this small mission to inform.

One of the pupils rescued me. "Mr Straw", he said, "isn't it like this? You were Home Secretary, now you're Away Secretary?"

Not bad, I thought. But if it was not so easy explaining to a group of schoolchildren what a Foreign Secretary did, how much more difficult will it be to set out what I do in my new job as Leader of the House of Commons?

But, for once in the arcane world of Westminster and Whitehall, the job title means what it says.

I have been appointed to lead the Commons, though not in the sense of telling them what to do.

Rather, as four times Liberal Prime Minister William Gladstone put it, "the Leader of the House...in great degree fixes the course of all principal matters of business, supervises and keeps in harmony the ambitions of his (or her colleagues)", and does much else besides.

The most regular public aspect of my job is an hour each week on the floor of the House for "Business Questions".

Formally, this is the opportunity for me to announce the business for the Commons for the following week.

In practice, this prime-time slot has long been used as an open-ended questioning of a senior government minister the only occasion in the Parliamentary week when this can happen, apart from the 30 minutes Prime Minister's Questions on the day before.

My open-air Question Times in Blackburn town centre have turned out to be excellent training for this.

Behind this regular weekly Commons appearance lies responsibility for the Government's legislative programme as a whole.

In democracies, all governments want to make changes in the status quo, so they have to change the law.

This means that a chunk of my time is spent planning the Government's programme in the Commons, working with fellow ministers to ensure they deliver their draft laws on time and in good order.

But the responsibilities go much wider than this.

One of the most fascinating aspects of this job is that you not only have to represent Government to MPs, but MPs back to Government.

During Labour's dreary 18 years of opposition, I well remember the Conservative Leaders of the House, like John Biffen and Geoffrey Howe, who for sure stood up for their party, but who also stood up for Parliament and us lot on the other side.