change nginx rewrite regex condition

I am not at home so i could not test it right now but something like this should work:

rewrite ^/answer/1/(www\.)*(.)(.+)/(.+)$ /answer/1/new.html break;
rewrite ^/answer/1/(www\.)*(.)(.+)$ /answer/1/$2.html last;

Let me explain: as stated in the nginx docs (here)

break
stops processing the current set of ngx_http_rewrite_module directives;

so if a request match the first rewrite rule (that is similar to your rewrite but ends with the /(.+) directive. This means that will match every request that was already matching but if and only if it is followed by 1 or more character after the slash. Beware of this because this means that the following url:

mydomain.co.uk/answer/1/www.aa// (yes this is a valid url)

will redirect to:

mydomain.co.uk/answer/1/new.html

if you don't want this beahaviour you can modify the regex as follow:

rewrite ^/answer/1/(www\.)*(.)(.+)/(([^/]+/?)+)$ /answer/1/new.html break;

here the (([^/]+/?)+) directive say: everything that is NOT a / repeated one or more time and that may be or not be followed by a /. all of this repeated one or more time.

I repeat, i am not able to test it right now but it should work as you expect. Remember that here the order of the rewrite url as i am testing FIRST for the url that should rewrite to mydomain.co.uk/answer/1/new.html and then there is your old rewrite that will still match the url but will not be processed by nginx since the break keyword of the previous rule.

edit: i confused last and break :)