Soldato
Not sure why I owe £300 tax to be honest considering my wage has only changed by £600 a year switching jobs, and also unsure how I take a £3450 drop unless they've done it to collect the money from the last 4 months but then £3450/12*4*0.2 = £230.
As above, looks like your previous employer has done some averaging of your deductions which then leads to arrears on starting your new job, or in my case occupational pension.
What's also annoying is they don't give you an option to pay the tax owed as a one off payment which I could have done quite comfortably out of my lump sum and left the code unchanged.