Slightly off topic however
It could be illegal but not for the reasons most people would think.
Im making a presumption that the crickets would have been 'feeder crickets' mainly used for feeding exotic pets.Thing is that neither of the two species used as feeder crickets are native species.
If so then releasing them could potentially be illegal under the The Wildlife and Countryside Act 1981 in relation to releasing alien and/or invasive species.
The link shows the relevant section of WCA for those who want to have a gander, in brief though it's illegal and punishable with either an unlimited fine or prison.
Extremely irresponsible and cruel in my personal opinion as releasing non native species is usually going to result in the death of said species. This could either be due to the environment being unsuitable for them or more likely them being exterminated/culled as a pest and/or invasive threat.