Confolens, a T trade in the trade lists is not the same as someone dealing on a T10 or T20 deal. here's what ADVFN define as a T trade:
'T' If reporting a single protected transaction.
A protected transaction occurs when a large order is going through the market. The buyer (or seller) may wish to keep the order anonymous from the rest of the market as the size of the order could greatly alter the price of the stock. With a protected transaction, the dealer will put the trade through in small quantities rather than knock the whole order out in one hit. The entire transaction is reported once the deal is completed. The LSE is notified at the start and at the end of the transaction. However, the market as a whole isn't told until the end, thus the order is protected.
What I find a mystery is how often a trade is marked T that really isn't all that big. But that's what their glossary says it means.