DB pension transfer cost

Albermarle

 Or are all DB schemes employer based so I would need new employment and an employer who DB scheme allowed transfers in.

Yes

The tax free lump sum is calculated by a formula  in line with HMRC rules . It is not connected to the transfer value .
Remember that your pension entitlement is always guaranteed and in line with the scheme rules , and the lump sum will be calculated on this basis.
 The transfer value can change significantly from one year to the next, as it depends a lot on financial market conditions at the time it is calculated.