Edit; this stuff looks like putty and can be used and painted like putty but isn't
https://hodgsonsealants.com/product-range/putty-glazing-compounds/heritage-putty/
Period Property sacrilege alert. I gave up on linseed paint for my joinery work a while ago - it's just too slow to dry to be practical - and switched to Bedec MSP, which is a microporous water based paint. This has been discussed elsewhere but is supposed to be very long-lasting and keeps the timber in good order.
This gave me a problem with using normal linseed putty, as the water based MSP will not paint over it until it is completely dry, which takes a long time. I could have tried painting over the putty with an oil based primer, letting that dry, and then painting over with MSP, but I'd heard good things about Repair Care Dry Seal so thought I'd give that a go.
It takes a bit of getting used to but I'm pleased with results so far, have used it quite a bit as both a bedding and face glazing for single glazing into sashes. You can buy it at Dulux Decorators Centres (I have to ask for it at my local one - it's not on display) or Sealants Online is a good source.
One of these is good for finishing it - as ever with sealants, the trick is to not faff about with it but to smooth in one action. Easier said than done sometimes!
Period Property sacrilege alert. ...a problem with using normal linseed putty, as the water based MSP will not paint over it until it is completely dry
Linseed putty needs to be prevented from drying out. The usp with Bedec is that it 'breathes'. That will dry the putty, crack, fall out.
Linseed putty - oil or linseed paint.
For my next project I'll be trying that Hodgson's. No use to the blue tits.