Spontaneous exchange of rulings: Legislative basis
IEIM530100: Spontaneous exchange of rulings: Legislative basis for exchange
Spontaneous exchange still requires a legal gateway, if a particular ruling may be foreseeably relevant to another jurisdiction you should check whether the UK has a Double Taxation Agreement, Tax Information Exchange Agreement, or other instrument for exchange with the jurisdiction in question. The UK has an extensive treaty network and it is likely that an appropriate legal instrument will exist.
There is a list of jurisdictions with which the UK has bilateral agreements Tax treaties - GOV.UK. It is also possible to exchange using the Convention on Mutual Administrative Assistance in Tax Matters; a list of countries where this convention has entered into force is here http://www.oecd.org/tax/exchange-of-tax-information/Status_of_convention.pdf. If in doubt contact JITSIC.
Within the EU, the exchange can be made under the Directive on Administrative Cooperation.