QGIS installation packages are all for v3, but this does not allow working with / importing OSGB1936 / EPSG27700 data, so I would like to install 2.18 if I can find an installation package. Any suggestions please?
Before trying to bypass, the issue you may look at you QGIS version. Some people encountered issues while using EPSG27700 but it seems to be fixed since QGIS 3.10.2 e.g https://github.com/qgis/QGIS/issues/33154#issuecomment-576350494 and another fix for another related issue has been done with QGIS 3.12.2 e.g https://github.com/qgis/QGIS/issues/35665
Otherwise, various options to install QGIS 2.18:
- Go the QGIS install archives e.g https://qgis.org/downloads/, download the file
QGIS-OSGeo4W-2.18.28-2-Setup-x86_64.exeand install. Be careful, the installer may conflict with your current installation
- Open in the Windows menu the OSGEO4W setup and look if QGIS 2.18 old packages are available (PS: was not able to confirm if yes/not, not anymore on Windows but remember it was an option to have more than one version of QGIS)
- Use Conda https://gisunchained.wordpress.com/2019/05/29/using-qgis-from-conda/ with a limitation in the composer e.g https://github.com/conda-forge/qgis-feedstock/issues/68#issuecomment-561228614
- Use docker with Kartoza qgis-desktop 2.18 image (see https://github.com/kartoza/docker-qgis-desktop)
I would go personally with second option and try the first option. The last 2 options are for "geeky" power users.