The RFU have a primacy of tenure rule which attracted the interest of the OFT and was legally tested by London Welsh. Laughably Leeds apparently signed a piece of paper which confirmed that Headingley's third club had primacy there - it was never put to the test and notwithstanding its existence RU games were occasionally moved for Leeds RL ones but never the other way around whilst they were in the top flight.
This document has a bit to say about the matter:
[url=http://www.farrer.co.uk/Global/Briefings/13.%20Sports%20Briefing/Analysis%20of%20the%20London%20Welsh%20Case.pdfAnalysis of the London Welsh case[/url
Quote [uGround Tenure and Ground Moves[/u: this concerns the ability of the clubs to use their home ground or grounds in order to meet the requirements of the fixture list and broadcasters, rather than the actual facilities required at those grounds (which are discussed in the next two sections). Central to this section is the concept of "Primacy of Tenure", which means that each club must be able to: (i) demonstrate that it can schedule home matches on weekends or bank holidays during the season at any time specified during fixed windows, and (ii) comply with the requirements of PRL's broadcast partner in televising home games. In order to prove Primacy of Tenure, a legally binding agreement to occupy the club's home ground or grounds must be in place for the following season, with the only pre-condition to the agreement being the securing of promotion.
The Criteria acknowledge that three current Aviva Premiership clubs (London Irish, London Wasps and Saracens) do not have Primacy of Tenure, but that no action will be taken for these breaches.
Primacy of Tenure does not mean that the club must be the main tenant at its home ground; while this was formerly the case, this requirement was overturned in 2003 by the Office of Fair Trading (OFT) following the blocking of Rotherham's promotion by PRL. This is important because financial realities dictate that, in many cases, a ground sharing arrangement with another sports club may be the only realistic choice for ambitious rugby clubs.
The OFT also ordered that clubs may use two stadia to meet the Primacy of Tenure requirements if necessary and so, while a club is expected to meet these requirements in relation to a nominated "Principal Home Ground" for the season, they may also nominate a "Standby Ground". Use of a Standby Ground requires prior approval from the PGB and, crucially, it must be located within thirty miles of the club's Principal Home Ground. Clubs may also nominate a "Temporary Ground" for one-off games – an example being the use of Twickenham Stadium by Harlequins for their annual "Big Game". '"
Quote What the appeal panel went on to consider, however, was whether or not the Primacy of Tenure requirements were compatible with competition law.
...the panel felt that it had been clear for some time before 2011 that the requirements were unduly restrictive, and so the RFU should have reviewed the position well before then – they could not rely on what amounted to a nine year old OFT blessing following the Rotherham case, not least because all other aspects of the Criteria had been reviewed on an annual basis since then. The panel therefore considered the Primacy of Tenure requirements to be in breach of competition
law and, as a result, unenforceable. The RFU's decision to refuse London Welsh's promotion was overturned and, inevitably, the Primacy of Tenure requirements will need to be revised. '"