Discounts go up and down, although towards the end of a Quarter (eg mid March) is a good time. Some dealers will need extra sales to reach Quarterly sales targets
There have been discounts of £1000-1500 plus extra £500-750 in the past, but that before the 0% came out (clearly if you are saving £2k in interest, will not get it off the price as well)
If you don't have a car to sell, brokers can sometimes get good deals, but again, they come and go, depending on what manufacturers want to shift.
Oddly the current 0% means not worth looking at nearly new unless you are getting about £4-5k off (especially if used interest rate adds £2k to cost in interest charges). Also remember the spec was revised last summer, some don't have the leather, or the digital dashboard
Quarterly sales targets create oddities, I once haggled for £4000 off a car, didn't get it as they said can't go that low, then following week, just into next month had identical car for sale pre registered on 31st for £5000 off. Salesman highly embarrassed when I pointed out they could have made extra £1000 if they had sold it to me week before, but as they wouldn't sell to me before, on principle I'm not going to buy it now. (It was a BMW dealer).