Visitor Visa 90 day rule

Hi there,

My parents (both Indian passport holders) are soon to apply for visitor visa with the UK Embassy in Chennai, India to go over to the UK to visit us in May/June. They wish to travel to the US before coming to the UK.

Current plan:
* They already have a US visit visa.
* They will apply for a UK visit visa in Feb. (I am a naturalised British citizen living in Manchester)
* They wish to travel to the US in the 1st week of March and head over to UK from there by end of May.

Will this travel itinerary cause any issues? I gather there is a 90 day rule (though I don't have a reference to a reliable source) which says that once a issued a UK visa one must travel to the UK with 90 days from the date of issue of the visa. - Is there such a rule in place? If my parents wish to stay in the US for a little over 3 months and then go over to the UK, will that cause a problem?

Any input on the above is much appreciated. If you are aware of such a rule, then any link to a UKBA resource / VFS resource would be useful.

Thanks.

There isn't any such rule. However, they must leave the UK before the expiry of their visa, unless they make an in-time application to extend.

They may request the effective date of their visa to be defered for up to three months. However, this request is often incorrectly ignored.