So what if you are an icon of childhood? Your message - always obey the boss - is just too depressing. It's time to shuffle off those mortal couplings
First, congratulations on your 50th birthday. And thank you for all the uncomplaining babysitting you have done in the past and for the amazed rapture you provoked in my son when we stumbled by chance across your little country place in Yorkshire - that siding on the Embsay Steam Railway to which you retire when the pressures of international stardom get too much.

But I can't, in all honesty, wish you many happy returns. In fact, I'm writing to ask you to think about an early retirement. You have been a really useful engine for Britt Allcroft, the television producer who bought your marketing rights - annual turnover around pounds 1.2bn, I understand - but what good do you really do the rest of us?

Moral instruction, you might say, but then your little world is instructive only in the most limited way: it suggests that disobedience will be followed by punishment, and that the punishment will be nasty. Remember poor Henry, walled up in a tunnel simply because he was a bit precious about his beautiful new paintwork? Walled up ... I ask you!

The lesson Henry learns is that it doesn't pay to cross the boss. And that, in truth, is all the morality you offer - a simplified version of Old Testament retribution, in which the best reason for being good is that the Fat Controller will find out if you aren't. Commit a mortal sin and you'll end up hauling coal-trucks for eternity; be a good little engine and you'll be given your own branch line.

You won't miss your friends either, if you can really call them that. They are boastful, peevish and envious to their very couplings. There isn't even anything joyful about their disobedience - it's just spite or laziness or arrogance. There's no altruism here, only original sin curbed by force.

In case you think I'm being hard, I asked my three-year-old why he liked you, hoping to discover what value system you had nurtured in that impressionable mind. "Because he's got two coaches," he replied. "So who do you like better, Gordon or Thomas?" "Gordon." "Why?" "Because he's got more coaches". I know it must hurt but ... out of the mouths of babes, you know. More coaches ... the perfect ethic of utility and self-improvement, of getting on by toeing the line and never questioning your superiors.

Your old friend the Reverend William Awdrey has grumbled at the expansion of your little world, following privatisation by Britt Allcroft. These days new rolling stock is needed for the toyshops, new storylines to feed the video market. The results, according to Mr Awdrey, have nothing to do with running a railway and everything to do with making money.

He's right, but why is he surprised? There was never any ethic but obedience in the books, and now there's a new Controller in the sidings.