I paid £20 for a Qualcast Electric scarifier from Ebay. It's brilliant, and you should see the huge piles of moss I'm getting out of the lawn, and how the grass has perked up in just three days. The settings vary from a leaf collector where the wheel and tines are higher to scarification where the tines scratch into the soil, approx 2 mm. I've been very tough on this lawn, the moss is thick, and I've worked with the lowest setting and still it's not getting through the moss for three or four runs in some parts.
I've ordered some Eco Lawn Seed which contains microclover and I'm hoping will a) feed the lawn, b) outcompete the moss, and c) help it withstand the rigours of a young and huge Bernese Mountain dog! I'll oversow with that and next year when it's well established I shouldn't be scrarifying two or three wheelie bins full of moss and thatch!
As the grass wasn't growing (thanks to thatch, moss and said dog!) I haven't even serviced the mower yet!