Let's say you earn gross £60,000. This makes you a higher rate tax payer. As a result your personal savings allowance will be £500 -- any savings interest above that level will be taxed, at 40%.
However, what if you contribute £1,000 a month to a workplace pension through auto-enrollment? Employee contributions, I mean. Well then is your 'effective taxable' income reduced by £12,000 to £48,000 and are you now no longer a higher rate tax payer, and does your savings allowance increase to £1000?
TLDR: Will increasing my workplace pension contributions to increase my personal savings allowance?