A deal to buy the buses was revealed earlier this month, with Transport for London (TfL) confirming that its board had approved the financing of the order for the buses, a familiar sight on roads around Ballymena during the test-drive process.
Wrightbus employs around 1,500 people in Ballymena - and the confirmation of available finance will secure the jobs of those deployed on the Routemaster production lines. Around 800 have been driven onto London's streets so far.
First Minister Arlene Foster said: “Wrightbus is a shining example of a successful indigenous Northern Ireland business.
"Innovation is a key element of economic success and Wrightbus has once again demonstrated their manufacturing credentials.
"This latest contract not only results in almost 200 Routemaster buses servicing London but it is a timely boost for the Northern Ireland manufacturing sector.”
Deputy First Minister Martin McGuinness said: “Wrightbus is a flourishing business and this latest contract puts them in the manufacturing fast lane.
"The success in winning contracts reflects the sharp Wrightbus focus on innovation and marketing which has resulted in it becoming a major player on the global market.
"This follow up order is testament to the quality of the hard work and skill of their workforce and the benefits to our economy will extend beyond the gates of Wrightbus."
Introducing the so-called 'Boris bus' onto London's streets has been a signature policy of London's flamboyant Mayor, Boris Johnson, whose tenure will come to an end in May.
Boris Johnson has said he will campaign for the UK to leave the EU as battle lines were drawn between Northern Ireland's politicians on what David Cameron has called one of the biggest decisions of our time.
Mr Johnson said he could not turn down this "once in a lifetime" chance to quit the EU.
He claimed Mr Cameron's renegotiation had failed to deliver fundamental change in Britain's relationship with Brussels.
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