A new offence of Failing to Prevent the facilitation of Tax Evasion comes into force on Saturday September 30th 2017. You will need to have “reasonable preventative measures” in place, so this is a time sensitive issue.
Speedy recommends implementing a PSL of vetted suppliers, so can ensure all the suppliers you have a strong compliance record. That obviously means disengaging from non-compliant suppliers.
And as you identify it also means ensuring your contractors have compliant alternatives in place. This may involve educating contractors who may not be aware of anything untoward in their current arrangements, which could be tricky.
The reason you must take these actions is that the governments want to put it beyond doubt that any company (or partnership) actively or passively enabling tax evasion (including ‘turning a blind eye’) will be prosecuted.
As to what you can do in your business ahead of the September 30th commencement, the government has published (draft) guidance. Divided into six-parts, the guidance explains not only the policy behind the new offences, but it also lists the processes and procedures that can be put in place to prevent “associated persons” of your business from criminally facilitating tax evasion