Great Western Coffee Shop

Various media reports state.
Found at Waterloo main line station, London city airport, and Heathrow air port.
Said to be small, improvised explosive devices in A4 size jiffy bags.
All have been dealt with by the police.

If you work in these, or similar places, please be careful. Almost all employers have a written policy on minimising danger from explosives in packages etc. It would be well to review such policies and to be cautious.

In the absence of any specific instructions, any suspicious package should be placed gently on the floor and the room, and immediately adjacent rooms then evacuated. Leave the room door open.
Ring the police, and wait in a safe place in order to give to the police as much information as possible about the package.

EDITED TOO ADD later reports state that the package at Heathrow ignited (rather than exploded) when opened.

The news report said there were Irish postage stamps on the package.

Yes, which whilst not proving anything, does perhaps suggest a dissident Irish Republican connection.
Reports that the Irish police are working with the Metropolitan police, again proves nothing but  does suggest a possible/suspected connection.
Bombs sent by post were a popular tactic of the IRA, but don't seem to be favoured by Islamic extremist terrorists.

Anti airport extremists seem unlikely to send a bomb to a railway station.
A disgruntled ex-employee seems unlikely to attack airports AND a railway station.
Simple criminal extortion would normally be confined to one business or to closely related businesses.

And there are many other possible motives and potential perpetrators.

Focusing on Irish republicanism is unfounded speculation.

Leave the investigating to the investigators.

Quite founded speculation really, seeing as the packages were posted from the Republic of Ireland. Much more likely than some bunch from elsewhere going to the bother of smuggling their stuff into the Republic just to post it from there and make it look like whichever version of the IRA did it.

A bit of a non-event whoever was responsible.  Great training for security personnel and police through, and a reminder that vigilance should still be kept very high on the railways.

Another similar device has been found, and made safe, at a university in Scotland.
Police are linking this to the three devices found in London.