I think I have an answer for you. I phoned the Department for International Trade (020 7215 4594 Option 4) who weren't particularly helpful except to say "it doesn't matter if you're a tourist - taking a thermal spotter outside the country counts as exporting it, if it is a controlled item". Thermals are a controlled item (see below) So you need a licence. I honestly don't believe that customs would care about a single thermal spotter (they'd be looking for crates of them, but by the letter of the law you need to get an export licence. This can be done here:
SPIRE - Export Licensing System
There is an open general licence (Open General Export Licence (Technology for Dual-Use Items - from June 2019) which covers the export of dual use goods such as thermals. There is a list of prohibited countries, but I suspect that your destination is not on them. This is what the Open General Licence requires:
"
official and commercial export documentation accompanying the items shall include a note stating either: (a) "These items are being exported under the OGEL (Technology for Dual-Use Items – from June 2019)"; or (b) the SPIRE reference (in the form ‘GBOGE 20XX/XXXXX’) of the exporter’s registration in respect of this licence, which shall be presented to an officer of HM Border Force if so requested;"
https://assets.publishing.service.g...hnology-for-Dual-Use-Items-from-June-2019.pdf (If you are wondering why EU states are on the prohibited list that is because there is a separate licence for exporting to the EU.)
If you look on the the
OGEL and Goods Checker Tools you will see that Microbolometers (i.e. thermals) are covered under the UK Strategic Export Control Lists> Retained Dual-Use List > ANNEX CATEGORY 6 > ANNEX.CATEGORY.6A. Alternatively type in microbolometer in the goods checker search.
Thermals are also covered under ML15d Open General Export Licence
Military, Security and Para-military Goods, Software and Technology and Arms, Ammunition and Related Material
ML15 Imaging or countermeasure equipment, as follows, specially designed for military use, and specially designed components and accessories therefor:
d. Infrared or thermal imaging equipment;