The contributions need to be made by the company and they can be paid to either a group personal pension scheme or an occupational scheme. As long as the contribution is made within the current trading year - ie must be debited from company account no later than last trading day of the companies financial year.
Personal contributions into a pension are restricted to 100% of their net relevant earnings, which cannot include any dividend payments but can include P11D benefits. However, if the Compnay/Employer contributes, then their payment is not measured against the individual members earnings, but this would need the satisfy the 'Wholly and exclusively' test as to whether it could be relievable against Corporation tax. Also if the Company/employer was to contribute over the members annual allowance, then there would be an annual allowance charge of 40%, and this would be borne by the member. Ouch.
From a tax efficient perspective, if company rewards directors by providing increase to income via a significant salary increase or one-off bonus payment, this being a trading expense will reduce corporation tax liability (check that from HMRC perspective, contribution can be deemed “wholly and exclusively for trade” and therefore the business can justify such a contribution). However, paying this by salary will increase Employee and Employer NI contributions.
If director elects to receive the “bonus” by way of pension contribution/salary sacrifice this will work to reduce both NI and Corporation tax liability, but to affect a salary sacrifice, there must be the salary in the first place. Make sure the reason for the bonus/increase in salary is noted in the company minutes to back up evidence as "wholly and exclusively for trade"
If the payments were made as pension contributions, there would be no NI to Pay, and therfore no NI to save, but so long as HMRC thought the payments satisfied their 'Wholly and exclusively' test, then the amount would be potentially relievable against Corporartion tax.
Hope this helps