Foreign spies in the UK might have to add their names to a register under a new espionage bill, Home Secretary Sajid Javid has said. It would aim to tackle threats from hostile states, he said in a speech at New Scotland Yard in London. He also said Syria and parts of west Africa could be designated as banned countries, with Britons who travelled there breaking the law. The new bill would update the Official Secrets Act and the laws on treason. He has also appointed Jonathan Hall QC as a watchdog to monitor the new terror laws. A register would act as a deterrent to spying and make it easier to take action against those involved, Mr Javid said. The home secretary said the tempo of terrorist activity was increasing, with 19 plots foiled in the UK in two years. The changes come after Britons in Syria asked to return to the UK. Shamima Begum - who had her UK citizenship revoked by Mr Javid in February - was found in a Syrian refugee camp after leaving London to join the Islamic State group when she was 15. Mr Javid said people travelling to, or remaining in, certain areas of Syria without good reason could face up to 10 years in prison. UK terrorism threat: How has it changed?Speaking to senior security figures in central London, Mr Javid set out for the first time how he expects to use the new Counter-Terrorism and Border Security Act. He said there were "real gaps" in legislation concerning so-called 'hostile states'. He said: "I've asked my officials to work closely with the police and intelligence agencies to urgently review the case for exercising this power in relation to Syria, with a particular focus on Idlib and the north east. "Anyone who is in these areas without a legitimate reason should be on notice." The north-western Syrian province of Idlib is the last remaining stronghold controlled by forces opposed to President Bashar al-Assad. Mr Javid said police and security services "have worked tirelessly" to identify people intending to join the Islamic State group overseas and prevent them from leaving the country. He told the House of Commons in February that 900 people people from the UK were estimated to have joined the Islamic State group in Syria and Iraq. Of those, 40% were estimated to still be somewhere in the region, 40% to have returned, and 20% to have been killed in battle. Mr Javid also emphasised the importance of international co-operation in combating terrorism. "As these threats become more global we all rely on an international system of defence, policing, security and intelligence - a safety net based upon co-operation and unity," he said. "These structures rely upon free, democratic nations to pool information, co-ordinate law enforcement action and surrender suspected criminals across borders." 'Long time coming'Sir Peter Fahy, former counter-terrorism lead for the Association of Chief Police Officers said the changes had been "a long time coming" but there would be complications over who it covered. Sir Peter agreed there was a "tremendous need" to reassure allies, adding: "The world is a very uncertain place at the moment... the whole issue about Brexit, this issue about Huawei and the situation with Iran is creating tension with the United States. "People involved in counter-terrorism will be looking to see if that does affect the level of co-operation."