The Premier League is stepping up it attempts to prevent pubs and clubs from screening live matches via foreign TV channels.

The League has been building cases against a number of premises in recent months over what it believes are breaches of copyright.

Around 100 prosecutions are being considered nationwide with the first set to be heard before the end of the month.

It is significantly cheaper for pubs and clubs to pay for foreign channels than it is to subscribe to the Premier League's official UK broadcasters, Sky Sports and BT Sport.

Foreign stations might also show matches not being screened in the UK, most notably those kicking off at 3pm on Saturdays.

In 2012, the European Court of Justice ruled in favour of Portsmouth landlady Karen Murphy, who had been using a Greek TV decoder in her pub.

Yet while the ruling made clear it was not illegal to obtain a TV subscription from anywhere in the EU, the Premier League were backed on issues concerning copyright.

The matches themselves are not protected by copyright, but any surrounding media works such as logos, graphics, pre-recorded highlights or the Premier League anthem are.

Any use of these without the Premier League's permission could therefore be construed as a breach.

Premier League spokesman Dan Johnson said: "We are stepping up our actions in this area and there are a number of reasons for that.

"One was the clarity we got from the Karen Murphy case in terms of copyright protection.

"It was written up as if we lost but in essence we won. It was a pyrrhic victory for Karen Murphy.

"A second reason is that we have just entered into a new contractual period with Sky Sports and BT Sport.

"It is important to protect the investment they are making in Premier League football, which not only benefits Premier League clubs but cascades right down the footballing pyramid to the grassroots."

A private investigations firm, ID Inquiries, has been working on behalf of the Premier League.

Johnson said: "We have committed to a significant number of visits and over the course of a season we will make approaching 5,000.

"We have undertaken nearly 4,000 and out of that we are looking at 100 prosecutions in the pipeline.

"We want to educate and discourage publicans from using these foreign systems.

"We will give the full information and give publicans and licensees the opportunity to cease using the equipment.

"If they choose not to then obviously they run the risk of being prosecuted."

Richard Munden, a barrister at 5RB chambers and an associate of legal advice service, can see how copyright could be infringed.

Penalties could include a fine, loss of licence or even jail, although much would depend on the individual circumstances.

Munden said: "If you have got a Greek decoder and can get the signal there is nothing illegal about that.

"The question is are you infringing copyright by broadcasting it in public?

"Prima facie yes you are. Not if this only applies to the game, the commentary or the crowd noises etc, but to any of the graphics, the Premier League anthem or any of the things that come up at half-time, that sort of thing."

In theory this could lead to a situation where pubs could attempt to cover up parts of the screen or turn down the volume, as then they would not be doing anything illegal, but that might not be practical.

From a legal perspective it also presents an intriguing situation where this could be considered as finding a loophole to counteract the other loophole the Premier League is relying on in terms of copyright.

Simon Clark, head of intellectual property at Berwin Leighton Paisner, said: "This is a curious loophole since the UK Copyright Act includes an express provision which states that it is not an infringement of copyright in a film or broadcast to show it in public to a non-paying audience.

"Perhaps some pubs will try showing the broadcasts with the sound turned down and covering up the parts of the screen which display the logos and graphics?"