As expected, the Airports Commission yesterday put the Mayor of London's pet project, a Thames Estuary airport, out of its misery and definitively ruled the proposal off its final shortlist. While this came as no surprise, the decision throws up considerable ramifications politically and for London taxpayers.

While hundreds of column inches have been dedicated to the impact of the decision, it is worth remembering the context in which Boris Johnson has pursued this vanity project. The Mayor first launched his brainchild in 2011, and architects' impressions of the airport have adorned newspaper pages ever since. Less reported, however, was the fact that none of the major players in the aviation industry ever got behind the proposal, nor did the local council, or other national politicians and experts, leaving Boris to act as the solitary cheerleader for the plans.

The inclusion of the estuary option in Davies’ interim report in December gave the proposal a temporary stay of execution, but resulted in a period of in-depth examination which led to four independent reports exposing major flaws with the proposal. These reports pointed to the huge environmental, financial and safety risks associated with the plans, with a headline £120bn price tag – the equivalent of building another eight Crossrails. This led Politics.co.uk to describe the scrutiny as "the final nail in the coffin" of an estuary airport".

In this light, then, the Mayor's decision – just weeks earlier – to sign off an extra £2m worth of expenditure on lobbying for his plans, showed tremendous chutzpah. Indeed, the extension of this allocated funding took the total envelope for the Mayor's lobbying exercise to £5.2m. At a time when any form of support for his proposals was sorely lacking and with the writing quite obviously on the wall Boris should not have been throwing good money after bad on further support for the plans.

On learning that the whole exercise has cost up to £5.2m, one is left with the sour taste that Boris probably knew the scheme was doomed to fail from an early stage, but ploughed on regardless because of the platform it gave him as a mainstream political figure. It has allowed him to posture as a blue-sky thinker when realistically his proposal never had a chance of solving the conundrum of airport capacity in the south east.

Whilst the Mayor continues to celebrate his doomed Estuary Airport, I think Boris Johnson owes Londoners an apology. In the time that he has splurged £5.2m of taxpayers’ money, Londoners have suffered years of inflation-busting fare rises, seen ten fire stations closed and now face plans for 900 jobs cuts on the London Underground.

What is more, instead of accepting the Commission’s decision yesterday with dignity, Boris had the audacity to come out fighting, saying that he would continue to lobby for an estuary airport as the long term solution. In light of the waste of taxpayers’ money I have written to TfL to ask if it will prevent Boris from spending any more public funds in support of an estuary airport now that it has officially and firmly been ruled off the Commission’s shortlist.

What hasn’t escaped the attention of politicos is the fact that yesterday’s decision might actually work in Boris’ favour. If Boris gives up the ghost and accepts that the estuary option is dead (as he may or may not do), it means that he no is longer left advocating the closure of Heathrow– a major local employer in Uxbridge – and the demolition of west London’s economy.

He can now oppose further expansion at Heathrow, but support its current operations – the perfect political fudge for an incoming candidate. What he cannot escape though, is the waste of £5m of valuable public funds – something he should now apologise for.

Val Shawcross AM is London Assembly Member for Lambeth and Southwark and transport spokeswoman for the London Assembly Labour Group