chudford wrote:

My Daughter has just bought an old house with oak beams that have been
coated in thick black paint/varnish.
Is there any way that they can be stripped back to the original wood
surface in situ without wrecking the surrounding ceiling?

It depends.

Builders will insist in sand-blasting beams to remove the old paint.
This is fine if you want to ruin everything inside the house and to
ensure that one will be eating sand in every meal for the next thirty
years.

I've found that gently wire brushing by hand produces the best results
but it is tedious work and will take several weeks to do.

Any mechanical means will cause damage to the beams and that seems a
shame.