Much has changed, not least the temper of Tory MPs. Today the party on the right approves of C4 - if not for its gay and lesbian content, then for its part in encouraging small business enterprise via the numerous independent production companies set up to serve it.
The creation of C4, under the aegis of Lord Whitelaw, is now viewed with increasing nostalgia as the last great act of altruism in British television. It was set up, after years of debate, not to make money but to appeal to 'tastes and interests not generally catered for by ITV' and to encourage 'innovation and experiment in the form and content of programmes'.
How different everything was a mere 10 years ago. Margaret Thatcher had not yet turned her attention to rationalising the ITV unions and introducing the values of the marketplace to British television.
'There's no way that Channel 4 could be set up now,' says Jeremy Isaacs, its first chief executive. 'The notion that you should give a new channel a particular qualitative charge and invite it to be different in particular ways is almost unthinkable today. After high tide, the tide goes out.'
Many people in public service broadcasting would say that the low-water mark was reached with the Broadcasting Act of 1990. C4 narrowly avoided outright privatisation. But from next January it will be divorced from the ITV companies, which up to now have underwritten its costs, and must start selling its own airtime in competition with them. C4's critics believe that the process of commercialisation is already advanced. They point to the scrapping of the gay series Out and late- night discussion programmes such as After Dark; the advent of Bob Geldof's juvenile The Big Breakfast; budgetary cutbacks in Film on Four, once one of the jewels in C4's crown; increasing reliance on American series and ITV repeats; above all, an increasing lack of personality.
Others take a less apocalyptic view: C4, they say, has merely grown older and grown up, along with many of the original radicals. 'The black, lesbian, radical lefties have all turned into small businessmen and women,' says Liz Forgan, C4's director of programmes. 'Now they talk about cash flow instead of conspiracy theories.' The channel has not escaped the recession: programme budgets have been frozen for a third year.
But neither side can answer the crucial questions: how will C4 adapt to its new, independent circumstances? And if the commercial going gets tough, how much of its famed 'remit' will survive?
When Mr Isaacs was appointed to run the channel at the end of 1980 he was given what some now describe as a 'golden brief'. 'He had the licence to depart from conventional scheduling wisdom and the brief to follow minority programming of all sorts according to his own intellectual whim,' says Zenith's chief executive, Charles Denton, who was shortlisted for the job.
Mr Isaacs's first group of commissioning editors - many of whom, like Ms Forgan, had never worked in television before - had 13 months to get the channel on the air. 'It was chaos,' says Mike Bolland, who was commissioning editor for youth programmes and later head of entertainment. 'It was also incredibly idealistic and that, more than the chaos, proved a problem when we got on to the screen. Each commissioning editor had a little dream to pursue. Which is why everything seemed to be incredibly left of centre when we went on the air.'
But in its seemingly haphazard and chaotic way, C4 established a genuinely new approach, now widely imitated. It proved that a far wider range of voices could be allowed to speak, in whatever tone they chose, without the collapse of democracy.
It proved there was an appetite for an hour-long evening news programme, that viewers' complaints should be treated seriously, that it was possible to revive the British film industry, and that a new generation of entertainers was waiting for its chance. Among the performers who owe their careers to C4 are Ben Elton, French and Saunders, Jonathan Ross, Clive Anderson, Harry Enfield, Hale and Pace, Ruby Wax and Anneka Rice.
Above all else, C4 proved that there was a totally new way for a TV channel to exist - not as a programme-making monolith but as a 'publisher' serviced by independents. The use of independents has been taken up by ITV and the BBC in their own cost-cutting policies, swelling the number of companies from around 100 in 1982 to 750 today.
The problem for C4 is that, with the same independents now turning out programmes for everybody, it has become harder to maintain the distinctive personality that was its original strength. BBC 2 has recruited some of C4's top talent and developed an innovative and often daring style of its own, taking the kind of risks that C4 did 10 years ago.
'There's very little now on C4 you can't see on BBC 2,' says Mr Denton. 'There's no longer the sense of excitement about what C4 does; it appears to have become more predictable. When you look at C4 over a four-week period it's still substantially different from the mainstream channels, which must mean it's following a fair bit of the remit. But I don't think it's doing it with sufficient pizzazz and confidence.'
Anthony Smith, former director of the British Film Institute and C4 board member, now president of Magdalen College, Oxford, says: 'The real question is whether C4 is continuing to pioneer at the same rate as in the early Eighties.' A lot of things have disappeared, which doesn't in itself mean C4 has sold out. But I worry they're not being replaced with comparable experiments.'
Michael Grade, chief executive for the past four years, is convinced that C4 still has a unique and evolving character. He points to Alan Bleasdale's GBH and a forthcoming series of plays by new writers produced by Bleasdale, the arts programme Without Walls and the prime- time documentary series Cutting Edge. His scheduling skills have helped to increase audiences to just over 10 per cent this autumn.
It is important, Ms Forgan believes, to attract more of those viewers who still see C4 as a 'difficult' channel by using accessible, undemanding programmes such as bought-in comedy and Italian football. She concedes that there is 'more MOR material' than in the past. The trick is to balance that with more demanding programmes so that C4's nature is not compromised. 'The whole trick of the next five years is going to be to get that right. The economic climate makes it more difficult, admittedly. But it's do-able.'
Channel 4 cannot afford to change too much, Mr Grade says, because 'our future depends on providing real choice for the viewers and therefore real choice for the advertisers'. Early signs are that advertisers will be enthusiastic; Renault has apparently committed 40 per cent of next year's spend to C4.
The channel's director of advertising sales and marketing, Stewart Butterfield, says that 'with sharpening of the edges' - such as has already occurred at breakfast time - C4 is a strong commercial proposition. The danger is of panicking and compromising its identity.
'We have to keep our nerve and be almost more of what we are,' he says. 'Given that other people are making radical changes - Carlton and GMTV replacing Thames and TV-am - we will be presenting ourselves as more of the same, of what you know.' It is a nice twist that the once-experimental multicoloured '4' now stands for substance and tradition.