Self Employed and drawing down down a pension - how does Tax and NI work? Confused!

Craighoy

Hi all - I will be 63 very soon and plan to take early retirement in the about two months time. I currently work as a technical sales advisor for an IT manufacturer and some of clients and business partners/ resellers have asked if I would be available for some consultancy on a per day basis. 

I hadn’t planned to do this - but a couple of days per month may be nice - earning, keeping my hand in and social.

I will be drawing down on my pension to live off and paying the appropriate tax on this - trying to keep just under the 40% threshold at about £49k pa. gross.
If I start doing some consultancy I assume I’d set up as Self Employed. I estimate it would be earning around £10k per year. 
How does the NI and tax work in this situation? 

Is this just classed as additional earnings?

Appreciate any advice 
thx