Legality of using 916.5mhz in the UK?

I have a Humminbird Smartcast RF15 wireless fish-finder/depth-finder system (US version) which operates on 916.5mhz.

As standard, the maximum operating range is approximately 30m and rather limited for my intended purpose, which is fishing at much larger distances. There are tutorials on the net, which claim to extend the operating range to around 200m by modifying the antenna length on both the transmitter and receiver.

I have read that the transmitting power of an unmodified unit is approximately 1.4mw.
Would modifications to the antenna length affect the transmitted power?

I have read that this frequency is illegal to use in the UK.

I have also read that it is not illegal...and these units have been cleared for import.

Looking here:
https://ukspec.tripod.com/spectrum.html#b854
... it states;
915=... reserved for future TETRA, Europe, to 921 (-45: 870-876) (esp 916-917, UK)
919.5=.. future Amateur, to 920= recommended by DSI2 for 2008

Wikipedia also notes the following authorities using TETRA frequencies;
Police, fire, NHS, armed forces, Highways Agency Traffic Officers, Civil Contingency Services, HM Coastguard, and misc. emergency services, Transport for London (London Underground)

Could someone please clarify whether this frequency is actually allowed to be used in the UK and if so, what is the maximum allowed transmitting power?

This page says it is reserved (916-917) in the UK for TETRA:
**broken link removed**

So I would guess not, but if you are only transmitting low range then I would plead ignorance if anything came of it, which, I doubt ever would as police bands etc are usually encrypted anyway.

Mickster,
What is your hat? I found a picture of a man that won the right to wear a colander as religious headgear on his Austrian driver’s license. see link
https://www.venganza.org/2011/07/austrian-colander/

It' not my hat Ron, it's a random pic from the internet, of a tinfoil hat & some other garbage on top...