Can you ferment to long?

I went out of town unexpected and it's now been 8 weeks of fermentation instead of 2 weeks can my beer go bad? I want to know if it's ok to bottle still. It's a english brown nut ale.

With proper sanitation and handling, the beer is fine. At worst it might've gone sour. Pathogens can't survive even minor amounts of fermentation. No worries.

I had a pale ale in primary for 10 weeks for similar reasons and it came out fine.

The other respondents know exactly what they are talking about. If you are very careful with your sanitation practices (and temperature control), you can easily get away with 8 weeks in the fermenter in almost all cases.

2 weeks is plenty for a lager fermented at 6-8 Celsius!  If it's high gravity then one might consider pitching with a higher yeast cell count.

A starter defintively helps, so does good aeration of the wort.  Maybe you consider adding some yeast nutrients at the end of the boil?

An ale should be done withing a week, two max.  If not then one of the above should help (you will get less nasty by-products).

It can remain lingering in the fermenter for longer.  But be careful you don't get autolyisis which can have a negative impact on flavour.

Hope this helps