I am very pleased with the result - it may not be pretty, nor as expert as a professional's would be, but the concrete (my first ever attempt at making it) has hardened well and I have been able to walk on it succesfully.
The path along the side of the greenhouse at the bottom of the steps is not finished yet as I ran out of concrete materials (it doesn't go nearly as far as I had hoped) but I have put the gravel base in, next just a fairly thin layer of concrete to stabilise it all and then I am done.
So here is how it looks.
No more scrambling, slipping and sliding down to the greenhouse. My plan at the moment is to plant a small lavender hedge along the side of the steps to soften the edges and then to put a trellis along the side of the decking and grow some small plants up there. I'm very pleased all in all.
I reckon the whole project has cost me £150 which is quite a lot, but I really couldn't have done it cheaper I don't think, the materials, quite simply, were expensive! Still I am sure a builder would have charged me at least £500 considering the amount of hours it has all taken, so I am very pleased to have only spent that much. I am quite keen to lay a path from the house to the top of the steps now and have plans brewing in my mind.