T trades are trades taken with extended settlements e.g. T+20 means you buy the stock but pay 20 days later. The idea is that you sell within the 20 days to make a profit and never have to stump up the money. The more T+ trading the more likely the share is to be volatile. If T traders get it wrong they often can’t pay up and are out of the game, if T traders get it right they can make money on money they don’t have. TD Waterhouse offers T+ trading, Selftrade doesn’t.
A spreadbet on the other hand is a bet with a spreadbet company, a T trade is shares bought on credit via a broker. You have to settle the T trade at the end of the period and you own the shares at the end of it, a spread-bet can be rolled to the next period and you never own anything.