Silverline Worktop Jig, £19.99 + VAT at Selco, don't do it:
https://www.diynot.com/diy/threads/silverline-worktop-jig.81458/
https://www.diynot.com/diy/threads/silverline-jig.25542/
Buy the proper gear:
https://www.toolstation.com/shop/Power+Tool+Accessories/d80/Router+Jigs/sd220/Trade+Jig/p72312
https://www.screwfix.com/p/trend-700mm-professional-worktop-jig/79077
https://www.diynot.com/diy/threads/silverline-worktop-jig.81458/
https://www.diynot.com/diy/threads/silverline-jig.25542/
Buy the proper gear:
https://www.toolstation.com/shop/Power+Tool+Accessories/d80/Router+Jigs/sd220/Trade+Jig/p72312
https://www.screwfix.com/p/trend-700mm-professional-worktop-jig/79077