Here's an interesting one. The US 457(b) plan is a tax deferred savings plan available to employees of US local governments, states and tax-exempt organizations. Contributions are tax deferred and grow tax free until distributions are made when they are taxed as income. In those respects they are similar to 401ks and 403bs. However, the distributions can be taken without penalty at separation from service.
So how does HMRC see the 457(b), is it a pension? If it's funded from US state or local government funds Article 19 applies, but which paragraph? Finally how is the savings clause applied to a UK citizen, US citizen and UK/US dual citizen permanently resident in the UK?