Police arrested the men after it emerged a significant amount of horse meat containing the painkiller "bute" could have been entering the food chain for some time.
Authorities in Britain and France are trying to trace the carcasses of six horses contaminated with bute - which were slaughtered in a UK abattoir and may have entered the human food chain across the Channel.
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Temperatures will feel a little milder compared to of late with highs reaching 14C (57F).
Dozens of common treatments to help with a range of ailments are apparently of little or no use.
The prime minister has offered Scotland, Wales and Northern Ireland a "direct line" to Brexit Secretary David Davis.