You are crazy if you drop from ~£50k to £17k.
Not only that but that's a very low starting wage for IT. I started on £18k fresh out of uni and my first ever full time job which was IT support, 10 years ago now.
Same with me but I skipped 1st line and went straight onto 2nd support starting at £18k 10 years ago.
Depending on area, starting salary should be at least £20k.