can I cover tarmac with soil and sew grass seeds

Hi Tricia I really wouldn't recommend covering tarmac with soil and then sowing grass seed. There will be no way for water to drain and the soil will become wet and sour. The only real solution is to dig up the tarmac first.

I wouldn't advise it - I know some people do it, though usually they break up the tarmac a bit to allow some drainage, but the resulting "grass" will be very poor, not to mention soggy, yellowing and damp during autumn, winter and spring. Tarmac's not usually very thick so often isn't that difficult to get up, unlike concrete.

I agree, with no drainage I think you will have problems trying to grow grass.
Have you considered artificial turf, shingle or bark? If it's an area you can put a frame round you could then fill it with shingle or bark and add some pots for colour.

Just remembered my garden centre sells strips of path. They are made of shingle stuck to a backing the strips are about 1" inch thick 2 ft wide and 5 ft long approx and are made for covering ugly paths etc . They are in several shingly colours. If you need more info let me know.

Both would still get seriously wet and the bark would simply decompose.

i dont think so, i agree with all above, no where for water to go,