What has happened in the United States?

The US communications regulator, the Federal Communications Commission, has voted for new rules which will allow media companies to own more TV and radio stations.

One company can now own TV stations which reach more people, and newspapers and TV or radio stations can now be brought under the same roof.

While some restrictions remain in place on the four biggest TV networks - ABC, CBS, NBC and Fox - the new rules replace laws last set in 1975.

Media companies saw those as "outmoded" in a country which now has thousands of cable TV stations, satellite TV, and the internet battling for people's attention.

Critic: Ted Turner has spoken out against the US changes

But critics say that allowing big companies to get bigger will stifle independent voices. One is CNN founder Ted Turner, who says he would never have been able to begin building his media empire if the new rules had been around when he started.

Why does this matter in the UK?

If the UK Government has its way, a similar relaxation of media law will come into effect later this year with the Communications Bill.

It will allow media groups from outside the European Union to buy UK broadcasters, it will allow radio groups to own more stations, and it will allow ITV to be controlled by a single company.

What could happen?

Channel 5 is at the centre of much of the speculation. It is currently owned by German-based group RTL and a UK company, United Business Media.

But pundits see a relaxation in rules as an ideal way of allowing Rupert Murdoch's News Corporation to snap the company up - something which is banned by existing laws.

Granada and Carlton are already planning to merge into one company, ITV plc - although competition regulators still need to approve this.

Presently, ITV is run by a federation of small regional operators, most of which are owned by Granada or Carlton. A merged ITV could itself then be bought out.

Rupert Murdoch could benefit on both sides of the Atlanic

Some of the UK's best-known radio stations could be changing hands too. Clear Channel, a huge US firm with worldwide interests in radio, concert promotion, concert venues, and advertising, is one of the companies which is likely to benefit from the new rules in America.

In the UK, it has already reportedly been eyeing up Classic FM and Capital Radio - known for its London flagship station as well as other names like Century and BRMB.

Alternatively, some of the UK's big radio groups could merge to fend off foreign takeovers - meaning more stations could come under common ownership.

Who's for it?

The government believes allowing the UK's broadcasters to merge will make them stronger, and boost the media industry as a whole.

For example, while Granada is a massive player in the UK, it is a tiddler compared with giants in US, or even in other parts of Europe. Allowing Granada to become part of a merged ITV would allow it to do battle with the world's biggest companies.

Who's against it?

Critics say the likes of Granada, Carlton, Capital, and other UK media companies would just be easy prey for giants like News Corporation or Clear Channel, or other US conglomerates like AOL Time Warner, Disney, or Viacom.

Craig David: His record company Wildstar is half-owned by Capital

Some fear the power that these companies hold - allowing Rupert Murdoch to own The Sun, The Times and Channel 5 would anger critics.

Musicians including Tom Jones and Billy Bragg say it could lead to a lack of diversity on the UK's airwaves if companies abuse their powers.

If Clear Channel bought Capital Radio it could control three London radio stations (Capital FM, Capital Gold and Xfm), one of its biggest venues (Hammersmith Apollo), one of the UK's biggest concert promoters (Clear Channel Live), plus a half-share in a record company (Wildstar).

In the US, Clear Channel has come in for criticism for allowing its radio stations to organise rallies to back the war in Iraq and ban music by bands which were against it, like the Dixie Chicks.

It has also been criticised for syndicating shows across its local stations - which some say stifles new, local talent.

What happens next?