J wrote:
"Cicero" wrote

If you hit metal at 10mm you've probably got a 'Catnic' lintel which
is a hollow steel box section. Try continuing drilling with a metal
drill for about about another 4mm and if your drill then breaks
through into a void it will confirm that you've got a 'Catnic'.

If this is confirmed you can attach your blind using self tappers
into the steel lintel.

I have tried drilling through the metal, but it seems very hard and
doesn't like me trying to drill through it, even a pilot hole.

That's because it's metal, have you tried a different drill bit? - there's a
possibility it could be angle iron, in which case it could be 10mm thick,
maybe you need some adhesive instead?