Hmm. From a Police point of view, the only criminal offence that could be committed is 'Public Nuisance', contrary to common law. However, for this to go anywhere, you would have to show mre than just what you have stated, e.g. caller is a repeat offender or the HEMS landing halted a football match. Wasting Police Time only applies to the police, and even if this were made out in these circumstances (such as lots of police turning out to assist, cordon HEMS landing site, etc.), the only section of the offence that could apply is 'making...false report...giving rise to apprehension for the safety of any persons'. Sadly, the CPS would never run with that at court.