benjaminfjones (44 mins ago) was right - OpenSSL was the problem - once OpenSSL was installed and I re-ran make it worked. (sudo apt-get install libssl-dev).
For the benefit of anyone with this problem - the complete list of installed packages for my (apparently successful) build in Ubuntu 12.04 is as follows. Im sure these arent all necessary! (but this could be used in troubleshooting by generating a similar list with dpkg --get-selections and running the diff command):