How to visit an institute when looking for job? I am a lab technician (microbiology &amp; molecular biology) and biology student, and I am currently seeking for job in some institutes in the UK. After sending my CVs to the HR departments, I usually got some replies with acknowledgement, or pointing to the institute's vacancies webpage, etc. 
Now I would like to be more proactive, and I feel like it would be good to visit some labs in person, meet the group leaders and other researchers, learn more about their research, and see how I could fit in these groups with my expertise. I expect this to be more efficient than sending CVs to the HR, as team leaders could know about me, and consider more seriously to hire me in their labs.

My questions are, is this kind of visit possible at all? How much I need to organise it, can it be kind of spontaneous? I know there are some other institutes elsewhere, where it is accepted, and they are happy if somebody just pops in to the lab to meet people and learn more about their work. Might this attitude be general? I am afraid they will find me intrusive. And how I should organise a visit, should I write to HR, or to the team leaders, or just drop in, say hello, telling that I can return later if the time is not appropriate?
Although many academics are not quite happy with the bureaucratic difficulties and delays caused by their HRs, HR departments exist not without a purpose. In the UK, the academic jobs should be advertised publicly and the appointment should be made on the base of merit according to pre-specified person criteria. 
If Dr Who uses his personal relations, or secret charms to persuade a PI to hire them, the following chain of event happen:


The post is created and formally advertised
100+ candidates submit their applications explaining how they fit the person specification criteria
Someone (an academic or HR or both) pre-screens applications and compose a short list
Candidates from the short list are invited to travel down to the University for an interview
Everyone is rejected, Dr Who is hired.


Before answering the "howto" question, please consider, if you think the whole process is fair to everyone involved, especially to other candidates?

Regarding your question, if a stranger enters my workplace "spontaneously", and demands my time and attention, I will probably feel uncomfortable. Some people may find this intrusive -- for the record, I am one of them. There are clear instructions on how to submit a job application, and "walk into the lab out of sudden" is rarely on this list.

However, it may be a good idea to introduce yourself politely to the potential PI. Usual rules apply here: it is better to send an email first, explaining your reasons and motivation clearly. If your potential PI is considering hiring new lab members, they will engage in discussion with you, invite you to visit them, and work out further steps to get you on board.