In enigma2 scanning, you can use whatever NetID you want. It does not matter in the UK. Just leave Net Id to 00000 (or any random number) in tuner config and forget about it. In E2 scanning, you have to make sure you have an updated cables.xml file.
The NetID matters when using ABM or Autobouquets Cable. Try 41069 then 40980 after you have newest ABM installed. This is because the cable delivery frequencies have been adpated. They used to use QAM64, but all are using 256 now.