concrete lintels which way up?

The pretensioned reinforcing steel in the lintels is off-centre and is intended to be fitted closer to the bottom edge (the edge in tension).

look at them the measurements are 35-30 and 55-45 to the centres on the 65mm and 100mm sides.

But shall i put them horizontal, or vertical with a gap between or buy a third lintel and put them vertical? [george]

They are only designed to go one way up - you need to find out where the reinforcing is fitted (look at the ends & you may see two raised 'bumps') and point this to the bottom.

they are 65mm for a reason, and that is so that it covers the same thickness as one course of brick, also, the 100mm edge is the same width as a brick, so it's fairly straightforward, without examining the reinforcing which way they go on the wall

Or check with a magnet. The short side will be vertical. TBH the only time I used one I didn't realise about the reinforcing and it worked OK. I *think* you will find that you lay the bricks on the "poured" surface (because the other three are potentially visible).

No, as others have said, the 100mm side should be horizontal. There's not a huge amount of strength in the lintel on its own. They're designed to work in conjunction with brickwork over, the lintel providing the tension and the brickwork the compression zone.

See

i didnt realise that - maybe i should use steel, maybe get building control maybe get a surveyor...

but i haven't planned exactly what i'm going to do on top of it...

thanks. [george]