HMRC don't have a presence at any airport their ports function was merged with port function of UKBA (Immigration) this became Border Force. Border Force is the primary Law Enforcement agency in the areas of Immigration & Customs, they also support the Police in Counter Terrorism and areas of policing. They also carry out functions in many other areas for other government agencies like Defra & NCA. The UKBA was disbanded 8 years ago. They are funded by HM Government the same as all Police services. Like the Police they have had savage cuts to staffing i.e. 50% of their staffing because of austerity. Whilst the U.K. pax numbers are increasing the queues have to increase you can't make officers appear from thin air. Now if you want to blame anyone, their address is 10 Downing Str, London. This is before the explosion of Brexit, which will mean millions more passengers will need to be interviewed before entering the UK. As this is BHX thread, it's an unfortunate situation that BHX, GLA & EDI are suffering the most as the dept has prioritised its spending at LHR, LGW and Calais.