If a company is being run in administration are contacts/agreements still valid ? For example, a service legal agreement.
Yes, they remain valid
However, the vast majority of contracts allow the innocent party to terminate them if the other party commits an 'insolvency event' like appointing an administrator. This is typically an active step that the innocent party must take; it doesn't automatically flow from the insolvency event.
In addition, a company in administration is likely to have breached the agreement by, for example, not paying their bills. This will also have consequences under the contract which may allow the innocent party to terminate.