St Helier Avenue is one of the better cycle features in Merton. Things get a little confusing when you get to the roundabout with Morden Hall Road/Morden Road, however.
Coming north on the west side of St Helier Avenue there is a shared-use path, taking you round the roundabout, across Central Road. Then there's this junction with Bayham Road:
Now there's a few interesting features here. The first is the 'no-entry' sign, preventing traffic on the roundabout from rat-running up Bayham Road. For a cyclist there is nothing to suggest that you cannot turn left into Bayham Road. But there is a 'one-way' sign further up, so that motorists coming down Bayham Road to the roundabout won't be expecting oncoming cyclists. Secondly, the 'give way' line on the road is at the roundabout junction, not just before the cycle lane crosses the road. That's not correct by the Highway Code, as normally the traffic coming from the right on the roundabout (or in this case cyclists on the pavement) should have right of way.
Having crossed Bayham Road, you can continue on Morden Hall Road, and just past the sheep-pen crossing you encounter this:
What on earth is going on here? There is a Dismount sign, but then immediatly a right turn onto the busy Morden Hall Road. Why would you dismount here? But in fact, 20 metres further on, past the bus stop, the shared path continues. So in fact, given that there's no 'No Cycling' sign here, the shared path does in fact continue past the bus stop. Yet the path doesn't narrow. There's no reason to dismount. In fact it would be stupidly dangerous to leave the shared path at this point, into two lanes of accelerating traffic, so why are the road markings suggesting you do so?
OK, so let's backtrack a bit and cross Morden Hall Road at the roundabout via the sheep-pen crossing. Having crossed, looking south we have this:
Yes, another Dismount sign - no, wait, TWO dismount signs, separated by 10 metres or so! So having dismounted, you have to dismount again? Now I'm really confused! But in fact, if you go onwards to the second Dismount sign, and look back, this is the view:
That's right - the section you just dismounted for is in fact a shared-use path!
OK, so we've just gone past two dismount signs. But there is no 'no-cycling' sign, so in fact you can continue on the pavement - given that Dismount signs are advisory only. Continue left down Morden Road on the pavement - still no 'No Cycing' sign, which is good, because Morden Road is very dangerous indeed to cycle on. Just before you get to Morden Hall Park entrance, look back and you see this:
Yes, it was shared-use all along. No dismount signs going the other way...however, at no point along the shared-use path is there anything to warn pedestrians that it is shared-use.
It's no wonder some people are whingeing about pavement-cycling - it's perfectly legal here, although you wouldn't know it!