Too late for this years pre orders now, but for a couple of years i used my work's 6% off Currys gift cards. Then used those gift cards to buy Apple gift cards from them, added them to my apple balance and then purchased the phone direct from Apple. Saved the 6% but benefited from Apple's customer service, guarnteed launch day stock etc.
Havent bothered this year though as it adds considerable extra faff over just going for 4% off Apple gift cards direct. Also the process wasnt always smooth, one stroe would only sell me £200 of apple cards as apparently theyd had issues with fraudulent purhases of Apple cards, tried to convince them otherwise but they werent having any of it so drove 20 mins down the road to the next one and thankfully they had no issue at all. Also I would buy them in £500 batches, so took 3 trips to get enough for the 1tb, for the sake of an extra £30 saving over the 4% (plus ive since moved and my nearest Currys is miles away) it hasnt seemed worth it this year, but maybe an option for someone next year that wants to maximise their savings or just something to do regularly to save on Apple One etc (i still do that as a way to get 6% off the subscription as it takes from your Apple balance before your bank)