Gosh, I have to put up the B.S. sign! :-)

For anyone wanting DAB and Line In while keeping the original stereo and not wanting to spend the money on a Grom, I've just bought one of these to put in her indoor's Merc https://www.ebay.co.uk/itm/254817833872. I had a couple of Sonichi s100 units (https://www.halfords.com/technology/car-audio/dab-car-stereos/sonichi-s100-digital-radio-adapter-342136.html), one in her car and one that I used in the company van which was recently put in the Ascot. The one in the Ascot packed up so I was going to get another when I saw the Autoleads unit. Just installed it and it is pretty damn good. Connects to the stereo using RF but encodes the station name to RDS so the car display shows the DAB station you are listening to. Has a small, very neat wireless control so no cables need to be run to it either. Her car already had a DAB aerial fitted so I used that but it even comes with an amplified aerial too.

Dear All,
If you don't want to have another aeriel in your car you could use this https://www.classiccarstereo.co.uk/shop/antennas-aerials/dab-adapter-module/ which converts your FM aerial to a DAB aeriel. It plugs into the cable from the aerial so could be mounted immediately behind your radio with the output plug going direct into the radio, rather than having it in line or where your aerial is.
Forgot to say, works brilliantly