Mr Lyons joins the bank on Monday as director of corporate projects. He will not join the board and will report to Ron Sandler, NatWest's new chief operating officer. His task will be to manage the group's transition from 13 business units into five, devoted to retail banking, corporate banking, global financial markets, cards and private banking.
The senior appointment is the second since Bank of Scotland launched its bid and comes after the chairman, David Rowland replaced Derek Wanless, the chief executive, with Mr Sandler.
Mr Rowland's strategy of bringing in people from outside NatWest to defend it against BoS's hostile bid has attracted criticism from some analysts. Mr Rowland said: "Bringing in new people frees things up and we're finding great ideas have been thought of already. NatWest is very good at planning. What it's not good at is decision-making and implementing. Mr Lyons' background is in savings and life assurance, an area that needs lots more attention, especially in how well sell our products,"
There would be further senior appointments, he said. However, none were in the pipeline as yet.
Meanwhile, the Bank of Scotland said it would not be responding to questions put to it by NatWest seeking to clarify its bid. "They're of no consequence," said a spokesman. "If you apply our cost-income ratio to their cost base you get a billion pounds of savings before you even get into synergy benefits. Admittedly, it's an academic formula."
NatWest's final defence document would contain more information to help shareholders evaluate BoS's bid, Mr Rowland said. "It will amplify what shareholders already have," he said.