Tottenham and Man United are in financial arms race behind the scenes – and the latest news may just mean that the battle is about to intensify. United’s revenue has climbed gradually in recent years but, in contrast to Spurs, has not shown any dramatic upswings apart from in seasons when they have qualified for the Champions League. One of the biggest drivers for both clubs is commercial income – that is revenue generated from sponsorship, merchandise and other non-football streams. United’s commercial income has risen from £197m to £279m over the last five season, a 42 per cent increase, whi…