A good portfolio can be created well before one goes into--let alone graduates--college. I understand the graphic design industry to be largely portfolio-driven, and it continues to confuse me that the IT industry isn't the same way.
On our blog we do a series of interviews called Hacker Jobs Meets... where we pose ten questions to CTO's, Tech Directors and start up founders across the UK and almost all place a significant amount of emphasis on the importance of having visible code prior to an interview.
You need to talk to a HR professional and understand how the master and servants act (as amended ) apply and who owns what.
Startups could be opening up them selves to legal attack by competitors if they are found to be looking at a competitors code.
The vast majority of employers (at least the better ones) like to review developers github/bitbucket repo's in advance. Everything in there is open-source.
Your master and servants act has literally zero relevance to my point.
This is direct from a very senior hr/ir Guy (our GC at the time) when we where discussing the implications of this for a colleague who had come up with some advanced algos for improving big iron systems - IBM used to get him in to consult for them as he was a Mainframe rockstar
And you don't know much about UK and US employment laws as most of it descends from the original M&S act as both countrys share the same roots for their legal systems.