Tom Kelly, the director of stakeholder engagement, insisted the £56bn project was running on time and on budget, and reiterated the Department for Transport's assertion that the delay to 2020 the Bill for phase two was designed to ensure HS2 can link up with any new potential cross-Pennine rail link.
He also defended six-figure salaries paid to one in four officials, arguing that HS2 needs to compete with transport projects globally.
But he admitted some of the £4.1bn already spent before construction has even begun could have been controlled more wisely.
Mr Kelly said HS2 does not foresee Brexit posing any problems for the project, arguing that two training colleges in Doncaster and Birmingham should ensure it can fill high-skilled engineering and other jobs.
“We don’t see a problem at the moment but it’s something that we keep monitoring,” he told journalists at a Westminster briefing.
HS2 was criticised last month after it emerged one in four of its officials are paid more than £100,000.
But Mr Kelly said the recent departure of Paul Griffiths, managing director of phase two of the project to Manchester and Leeds, showed HS2 needs to pay "competitive salaries".
“We are operating in a highly competitive field, our phase 2 director has just been poached to head up a major infrastructure project in Toronto," he said.
“This is a global business.
“Secondly however those 7,000 people we employ at the moment, they are all taxpayers, they will all be contributing tax to the local economy, the 15,000 we will employ in 18 months will do the same, the 30,000 we will employ in five years time, they will do the same.”
He added: “The amount of salary we have to pay is decided by the market, we can’t order people to work for HS2.”
Mr Kelly admitted that HS2 had not kept tight enough control of spending in the past but pointed to a National Audit Office (NAO) report from last week which said the project was improving.
“At times our processes have not been what they should be but as the NAO said last week our processes are improving and have improved considerably, we are learning lessons," he said.
“That’s the same as every single infrastructure project, you learn lessons as you go along.”
Mr Kelly also criticised the "myth" of the "either/or mentality" in which people demand HS2 is scrapped and the money spent on upgrading existing routes, saying the DfT plans to spend £43bn on the existing network until 2033/34, and pointed out it is more difficult to upgrade existing lines.
He said cities like Leeds are already feeling the benefits of HS2, which he said is driving economic regeneration.
“If you look at the plans they have got for the South Bank, it’s entirely built on being close to the station and using that to completely regenerate that side of the city," he said.
“All I can say is I think Leeds have been very, very proactive in the way they have used HS2 not to develop that South Bank area but the technology area that is going to be around our depot as well."