Others, however, have asked very pointed questions on the question of platform neutrality. It came up at the Public Accounts Committee I recently attended, and I have (quite properly) taken quite a grilling from MPs representing the views of constituents deeply concerned that on launch, BBC iPlayer focused on a Windows-based solution.

I've just responded to a letter on exactly these lines. My reply gave me an opportunity to explain the BBC's position - why we made the decisions we did, where we are now, and what our plans are for the future. I thought it worth posting the substance of that reply here, in blog format - not least because it includes what I hope is good news for Mac and Firefox users in particular.

The first thing to say is that - contrary to what some believe - the BBC actually works hard to provide internet services on a "platform agnostic" basis. The BBC iPlayer has made programmes available to Mac users and users of other operating systems via streaming since December 2007 - a move which I'm told has gone down very well indeed. However, the issue of download of programmes to Mac and other platforms has always been a more complex issue for technical and rights reasons. Our response to those challenges has been the subject of much debate and conjecture and I'd like to do what I can to clear this up here.

The BBC has, however, always been committed to exploring alternative DRM systems with Real Media, Adobe and Apple and we are part of a consortium looking at developing alternative, cross-platform DRM systems. As many people reading this will know, the application to the BBC Trust for approval of the BBC iPlayer expressed the hope that we would be able to provide a platform neutral solution within two years - although it has to be said that the BBC is also dependent on the cooperation of third parties to achieve this.

The Trust recognised the practical difficulties facing the BBC but required it to report progress on a six-monthly basis. Work is still ongoing, but I am happy to be able to confirm here that we are aiming to launch a download version of BBC iPlayer for Mac this year. I can also confirm that Firefox users are now able to download BBC iPlayer programmes. I hope this good news is evidence of the hard work that the BBC is committing to supporting other platforms.

Ultimately, the BBC has had to balance our desire to achieve platform-neutrality against:

• the demands of our rights holders
• the viability of alternative technical solutions
• value for money to the licence-fee payer.

At the time of the development of the BBC iPlayer, the BBC was forced to choose between offering the service to a majority of users immediately - or to not offer catchup TV over the internet until full platform neutrality could be achieved. We chose to begin by serving the greatest number of licence-fee payers possible, and to follow up on that work to extend the service to other operating systems at the earliest opportunity.

I'm told that analysis of our streaming stats (since this service is available to all users, it is considered an accurate representation of actual market penetration of those wishing to play BBC content online) shows that 90% of those users are running Windows, as opposed to 9% Mac, and 0.8% Linux. Given therefore that some 90% of people playing BBC content as streams are on PC, we estimate that our PC-only download solution is currently reaching 90% of the target audience.

I recognise that to many people's minds making this service available to only a proportion of users was not the correct decision, and I accept that for some there is nothing I could say to justify this choice. I hope, however, that those people might at least appreciate why the BBC believed that making the service available in the shortest time frame to the greatest amount of users was the most effective and responsible way of serving our licence-fee payers.

It goes without saying that the BBC must always act in an entirely responsible manner with the limited funds at our disposal. However, I think it is fair to say that a certain degree of pragmatism will always be necessary when we consider how best to employ those funds. Were we to choose to not develop any systems or services until they could be received by every single individual licence-fee payer, our capacity for development and innovation - in the interest of serving those who fund our services - would be severely limited.

I hope that this post has at least gone some way towards explaining the decisions made by the BBC in launching the BBC iPlayer, and that it makes clear our primary aim: to serve as many licence-fee payers as possible as effectively as possible. I believe that on this score the BBC iPlayer more than delivers, and I hope you will agree.

Mark Thompson is the BBC's director general.

N.B. Clarification 4.13 p.m. The phrase "Firefox users are now able to download BBC iPlayer programmes" above means that Firefox users can download programmes on their PCs, not on all platforms. Nick Reynolds (editor, BBC Internet Blog)