The filter you mention is for a Disco 1, your profile says you have a Disco 2. You need an LPX 100590 for that.
https://www.jgs4x4.co.uk/discovery-2-defender-td5-engine-oil-filter-genuine-lr/#:~:text=Discovery 2 & Defender TD5 Engine Oil Filter MAHLE OEM&text=Equivalent to Land Rover part number: LPX100590.
The rest of this may then be immaterial.
But if you DO have a D1.....
Did you smear a bit of oil on the rubber seal when you fitted it? Did you make sure the seal came out with the old filter when you took it off? They do usually come out with it, but you never know.
I'd put a pair of rubber gloves on, tighten it up as tight as you can by hand then wipe it off and do what you have just done. If it is still leaking I'd let it cool down and the oil drain back into the sump, then take the filter off again, which will be a bit messy and investigate the seal situation. It is just possible there will be two in there. The one attached to your new filter and another one left behind in the past. If it was fecking hard to get off, it could be because the previous owner had the same problem but cured it by tightening it up to feck.
Failing that we are into the realms of distortion or scratched sealing surfaces.
Does any of this help?
