THE MEDIA regulator Ofcom has now launched an investigation into the obscene answering machine messages broadcast on the Russell Brand radio show. Mr Brand and fellow presenter Jonathan Ross get laughs by offending against common standards of decency and in doing so, are in constant danger of undermining those standards. With their crude calls to much-loved comedy actor Andrew Sachs, aged 78, they went too far. Their editors should have stopped the broadcast, which was pre-recorded, and the BBC should have apologised much earlier and much more fully than it has done.

The BBC Trust, doubtless hoping that the hail of complaints will soon die down, is refusing to comment until a formal report on 20 November. But the corporation cannot hope to evade its responsibilities by delaying. The chairman of the Commons media select committee, John Whittingdale, is already calling upon BBC director general Mark Thompson to explain what went wrong. Former deputy director general Will Wyatt has condemned the episode.

It has emerged that Mr Sachs was asked by a junior producer whether he wanted the material to be broadcast. When he refused, the programmemakers used it anyway. That shows contempt for the audience, just as the faking of winners for Blue Peter and Children in Need competitions did. Now that every household has to find £139.50 a year for a TV licence, regardless of how little BBC output they may watch or hear, that kind of disrespect for the paying public goes down badly. As part of the BBC's stated mission to rebuild trust after the faked winners affair, the corporation owes it to the public to come clean about how this broadcast was allowed to air.

Andrew Sachs, as Manuel in Fawlty Towers, was part of some of the greatest British comedy ever, whereas Jonathan Ross is colossally overpaid at £6 million a year for a job fresher and younger presenters would do for much less - and Russell Brand's taboo-busting stunts are becoming tedious. The BBC needs to be much more open about what went wrong in a case where editorial controls clearly failed. It must also show that it is taking seriously the need to apologise promptly and fully rather than kicking the ball into the long grass.

Boris's towers

The decline in commercial property values means, as our Architecture Correspondent Rowan Moore explains today, that Boris Johnson has a breathing space in which to set out his priorities for London's skyline. So far, expectations that his would be an anti-skyscraper regime, shaped by his deputy Sir Simon Milton, formerly leader of anti-tower Westminster council, have taken a knock with Mr Johnson's blessing for the Three Sisters proposal near Waterloo. The stubby towers would impinge on some views of the Palace of Westminster. However, as our report on regeneration plans makes clear, the still-scruffy areas around the station urgently need improvement. The Mayor needs to explain why he thinks the Three Sisters will help achieve this.

As for the Mayor's other planning priorities, a lower target for tree planting is fine as long as it is actually delivered. Devolving the job of proposing new urban green spaces to the boroughs, while supplying the funds, should mean more parks where people most need them.

Clearly the Mayor has quite a lot of thinking still to do, on his housing policy in particular, but he should treat the slowdown as an opportunity to shape big schemes intelligently. Developers under pressure can no longer call all the shots.

And celebrating...

The Byzantium exhibition which has just opened at the Royal Academy is not just an opportunity to see some wonderful artefacts, icons and mosaics. It also lets us reassess our view of one of the great empires, which lasted a thousand years, yet has been associated since the Enlightenment with intrigue, factionalism and resistance to change.