Here is the type of trade it was according to the LSE
LRGS' (RTS 1) Post-trade large in scale transaction flag Transactions that are large in scale compared with normal market size for which deferred publication is permitted under Article 14.
Just spoke to Hargreaves & Landsdown, they have confirmed the cut off for owning shares is 1st October. There are no 'settlement' days, so you can buy shares on the 1st and still qualify.
'The Rights Issue is expected to open on 02 October 2018 and will be available to all Shareholders as at close of business on 01 October 2018. If you hold Shares at this time you will be entitled to purchase 3 new Shares for every 7 Shares held, at a price of 21p per Share'.