Janet Tweedy writes
Could I grow say two cordons to complement a proper tree?

Yes. There's no difference apart from the flowering time. Make sure they
are all in the same flowering group

IIRC Bramley is the one that doesn't provide viable pollen, so you need
a pollinator for it (which you presumably have in the area if it's
already fruiting) and a pollinator for the pollinator - ie don't rely on
the bramley to pollinate your new trees. But check first, because I may
be misremembering!

We were thinking of growing a fairly large tree where we had to cut
down the red oak this year. We could take up to 18 foot. We DO eat a
lot of apples, especially if they are Worcester's

Remember Worcesters don't keep for very long (though they are wonderful
if allowed to ripen on the tree. You might want to complement it with a
couple of varieties which will keep till autumn or spring.

I would consider having the tree as a keeping variety (you have longer
to eat the heavier crop), but I don't know how Worcester does as a
cordon.

Even a small tree can give 70lb of fruit, and our mature tree in
sevenoaks managed 400lb in the year of the hurricane, upon which it blew
over, depositing the entire 400lb on the ground.
--
Kay