Yes - and no! By definition loam is made from grass turves that have been stacked for several years and then sieved down into 'loam'. In practice, the only way to get decent loam now is to dig up your lawn and make your own. So, for practical purposes garden soil will do just as well.
The above seems to be a reasonable recipe for seed sowing although I would use grit rather than vermiculite, everything else is organic.

Many thanks Bulba. I have just been reading your blog re your recipe. Whilst I don't think I'll be allowed by OH to cut up my lawn I found your blog very informative. I have my leaves from last year rotting so may be able to make my own recipe later in the year. My leaves are beech leaves and I did recently read they take 2 years to become useable. Not sure if that's correct. Thanks again