According to your list the following still have intact holdings, unless I've missed something:-
3.1%----Legal & General,
3.2%----Lakeway Capital,
3.0%----SAB,
3.1%----Prudential,
3.1%----Abrams Capital,
2.8%----Whitmer
18.3%---Sub-Total
The following may also each have up to 3% due to going only slightly under the declarable threshold rather than making a complete disposal.
3.0%----Lone Pine Capital LLC
3.0%----Blavin & Company Inc
3.0%----Morgan Stanley Securities Limited,
3.0%----Eminence Capital LLC
3.0%----Deutsche Bank AG
15.0%---Sub-Total (Maximum)
Plus your original reckoning:-
6.9%----Southeastern Asset Management
11.8%---Barclays Plc
6.0%----Fidelity International Limited
5.7%----Goldman Sachs Group Inc
3.7%----Standard Life Investments Ltd
4.0%----Artisan Partners Limited Partnership
38.1%--Sub-Total
This makes a possible total of Min 56.4 % up to Max 71.4%
No wonder the buy-back had such an effect on the remaining SETS-traded free-float.