I'm assuming in this reply that your Standard Life pension is an Occupational Pension Scheme ("Company Scheme").
You have three choices: -
(1) Leave it in the current scheme, where it will continue to be invested, then draw your benefits at retirement. You will need to contact the scheme trustees when you want to retire, which will require you to keep track of them in the meantime.
(2) Transfer it to another Occupational Pension Scheme if you are/become a member of another one. Check up on charges and fund choices on both sides before deciding to do this.
(3) Transfer to a Personal Retirement Bond ("Buy Out Bond") with a provider of your choice. You choose the provider and the fund and have control over the investment of the pension fund thereafter. If you do this, you no longer have to maintain contact with the scheme trustees. Again, check up on charges and fund choices on both sides before deciding to do this.