The string "(alternatively the RSS feed can be customised, within" occurs at templates/web/default/alert/_list.html:25 and again at templates/web/fixmystreet/alert/_list.html:28, and another string is concatenated after it ("2km", "10km" etc.)
String concatenation is a nightmare for translators. :) The elements of the sentence won't necessarily come in the same order in other languages, or they might need to add (e.g.) suffixes to certain elements.
Ideally, for translation purposes, each string should be one "unit of meaning" — generally a full sentence, or a couple of short sentences.
Please could you change this to include a %s tag, rather than concatenate strings. Oh, and do the same everywhere else that strings are concatenated too. :) Ta.
This is not displayed as you imply - see http://www.fixmystreet.com/alert/list?pc=GL502PR - the single list of distances is given after the initial text, not each one in turn. I agree this should be done as one string, but just wanted to check that simply having all of "(alternatively the RSS feed can be customised, within 2km / 5km / 10km / 20km)" would be okay.
Ah, I see. Still much better as one string, as you say: "(alternatively the RSS feed can be customised, within %s)" would seem to be the best way forward. It's helpful — always — if there's a translator's note giving an explanation, or just an example, of how the string looks on the site.