If one of the large holders dumps their shares doesn't mean there's not a buyer. It's most likely they will find a buyer outside the market place anyway and recorded as a RNS.
irrespective of whether they sell to another institution or not, the trade/s HAS TO BE reported and displayed for ALL to see - its called transparency. An RNS/s would ONLY be issued :
1. If the SELLER held more than 3.00% at the time and the sale would mean they would no longer hold a notifiable amount
2. If the SELLER held more than 4.1%, they would only inform IF they sold 1% or more
3. The buyer would only issue an RNS if their stake is going result in a 3% or more holding
4. If the buyer already held 3% or more, then they would only issue an RNS if they were buying 1% or more.
Either way, ALL trades HAVE TO BE REPORTED on the screen. Its not only an FSA/LSE regulation but also an EU directive. They have to be shown on the screen for all to see (eg via LSE 3rd part vendors...ie ADVFN, or via virt-x 3rd part vendors ie bloomberg)