LONDON (Reuters) - Santander's UK chief executive Nathan Bostock will have his pension allowance cut from next year, as the bank becomes the latest to bow to investor pressure to rein in executive pension perks.Bostock's pension allowance - which was worth 588,000 pounds ($754,404.00) last year - will be reduced from 35% of his base pay to 22% in 2020 and to 9% in 2021, a source familiar with the matter said. That will equate to a cut of more than 400,000 pounds over the two years. He received a..