The four were arrested under anti-terror laws and are accused of owning computers, radio equipment and high-power magnets for terrorist purposes. They were to appear in court in London later in the day, said a spokesman.
The men were arrested under the Terrorism Act 2000 in the last two weeks as part of a long-term police investigation into activities linked to the Tamil Tigers, an organization banned in Britain.
Three were detained at the end of April in dawn raids at homes and business addresses in Wales and London. A fourth was arrested this week in the Swindon area of southwest England.
All four have been charged with conspiring to receive equipment for terrorist purposes between January 2003 and December 2006.
Other items which they are accused of procuring include laptops, head torches, circuit boards, lithium coin cell batteries, GPS (global positioning systems) and antenna equipment, transceivers, radios and navigation systems.
The four men were named as Arunachalam