Tree Creeper ?

[nightshade]

I was watching a bird (without bino's) it was working its way up a tongue and groove outhouse door following the grooves, it then flew to a walnut tree and again started at the bottom and worked up following the underside of the tree limbs.
I thought at first it was a nut-hatch but came to the conclusion it must be a tree creeper colouring was dark on top yellow underside

[Lincs Yellowbelly]

Most probably, the Tree Creepers i've seen have all started at the bottom and gone upwards, whereas Nuthatch tend to go down You always see something when you don't have Bins)

[glsammy]

I've seen blue tits do very convincing Tree Creeper impersonations! Could perhaps explain the yellow underbelly?