Hi Baz,
Buy colbalt ones, but they are not cheap;
https://www.orbitalfasteners.co.uk/e...balt-bits-a777
Unfortunately the general public (ie. non trade who have no idea what proper engineering costs are) think that B+Q or Screwfix gold drills are actually what an engineering firm might use
Also look on the bay for used older sets, over the last few years I have acquired full sets of British made metric / imperial / letter and number drills, all for a fraction of their value by being patient. Well looked after or little used sets often pop up on there.
ATB, Ed