[XAP]Bob wrote:"You may feel safer walking your cycle round on the pavement or verge. Else you should ride round keeping to the left-hand lane and [...]"?
Something like that.
IF is not exclusive (i.e. there are further options)
ELSE is exclusive (i.e. there are no further options)
The use of the word, "if," makes it a conditional statement, though. The "further options" you mention amount to walking round the edge - as per the first sentence. These two sentences are giving the cyclist two options: walk or cycle. It's saying that should you choose to take the cycle option, you should do so, "keeping to the left-hand lane."
Again, if the authors were saying that cyclists should not cycle round the roundabout in the left-hand lane, then wouldn't they just say so? If they were reluctant that we should do it that way, then why give it as an option at all? Why would they say, "Here's the most dangerous way of negotiating a roundabout," and then proceed to give us instructions in how to do it, thus endangering ourselves and other road users?