Britain’s terror threat level is being kept under “very close” review amid concerns that extremist groups could target Jewish institutions in the UK, a day after German prosecutors said they had foiled a Hamas attack plot by making four arrests. MI5 and counter-terror police indicated they were focused on whether the war in the Middle East could galvanise extremists into taking violent action, as Israel’s intense bombing of Gaza extends to its third month. The UK terror threat is now judged to be at around its lowest level since 2006, when the current grading system was introduced. It is formally rated as substantial, the third of five tiers, meaning an attack is considered likely. The threat level is the responsibility of the Joint Terrorism Analysis Centre (JTAC), a cross-Whitehall body based at MI5 – and is being “kept under very close and regular review” at the moment, one insider said. On Thursday, German and Dutch police arrested four people on suspicion of being part of a cross-border Hamas terror plot that German prosecutors said aimed to obtain weapons to target Jewish institutions in Europe. The four began searching for a hidden cache of weapons in Europe from the spring, according to German prosecutors, trying to find it repeatedly during October on the orders of Hamas leaders said to be based in Lebanon. Hamas has not traditionally sought to attack targets outside Israel, but German press reports said as many as 450 people associated with the group were based in the country, sometimes seeking to spread propaganda or solicit donations. Coordinated terror plots in the UK and continental Europe would represent a departure for the group and would be in theory a return to a type of attack not seen in recent years. Terror attacks since the London Bridge incident in 2017 have predominately been conducted by radicalised lone actors. Previously, when the MI5 director general, Ken McCallum, warned in October that the likelihood of a domestic terrorist attack could rise as a result of the crisis in the Middle East, he emphasised the threat from “self-initiated” individuals acting in “spontaneous or unpredictable ways”. One expert said the German plot appeared not to represent a serious threat to safety. Lord Ricketts, a former UK national security adviser, said “the good news is that the intelligence community evidently had full visibility of the planning”. But the ex-official added the threat to the UK and elsewhere was likely to have risen. “It’s common sense that there must be a heightened risk both of Islamist groups like Hamas activating other plots in European countries including the UK, or of self-radicalised loners deciding to act. I’m sure the counter-terrorism community is on high alert.” No terror attacks have taken place in the UK since 7 October, but earlier this month a German tourist was killed in Paris and two others injured in a knife and hammer attack near the Eiffel Tower by a 26-year-old man who had sworn allegiance to Islamic State at the beginning of December. Jewish groups in the UK said the reports from Germany would inevitably unsettle people in the community, although they added there was not thought to be any specific threat in Britain at this time. The veteran Labour MP Margaret Hodge said: “Wherever I go now within the Jewish community, it’s obviously concerned with Israel, it’s absolutely top of their agenda, but there is a fear that it’s affecting us here in the UK. So what happened yesterday simply adds to that.” The politician emphasised it was important for all communities to feel safe. “Certainly when I talk to my Muslim colleagues in parliament they too are facing threats so it’s not one-sided. Both sides are being frightened,” she added. Hate incidents recorded by monitoring groups against Jews and Muslims have soared since 7 October, with the Community Safety Trust recording more than 1,000 antisemitic incidents in the following four weeks. Reported Islamophobic incidents rose sevenfold, according to the Tell MAMA project. Counter-terrorism police said they were receiving a higher number of calls and reports to the UK’s anti-terror hotline but the level has dropped from the doubling seen in the initial period after Hamas’s deadly attack on Israel. Tim Jacques, counter-terrorism policing’s senior national coordinator, said: “Stats wise, we’re still seeing an increased level of reports compared to the same period last year – but not running quite as high as they were in the fortnight directly after the attacks on 7 October.”