You have a type C Business Visitor Visa which you have used once. Your entry clearance is marked as MULT and it expires in April 2015.

You want to reenter the UK to attend another interview. This situation is addressed in Paragraph 20A (Non lapsing leave) of the rules…

Leave to enter or remain in the United Kingdom will usually lapse on
the holder going to a country or territory outside the common travel
area. However, under article 13 of the Immigration (Leave to Enter and
Remain) Order 2000 such leave will not lapse where it was given for a
period exceeding six months or where it was conferred by means of an
entry clearance (other than a visit visa).

To interpret this… You have left the common travel area. You were not given leave for a period exceeding six months. Your leave WAS conferred by an entry clearance, but it was conferred by a visit visa. This amalgamates to the conclusion that your leave has lapsed.

However, since your entry clearance has not expired. Paragraph 31A kicks in, which says in part…

Where a person has arrived in the United Kingdom with leave to enter
or remain in the United Kingdom which is in force but was given to him
before his arrival, he may apply, on arrival at the port of entry in
the United Kingdom, for variation of that leave. An Immigration
Officer acting on behalf of the Secretary of State may vary the leave
at the port of entry but is not obliged to consider an application for
variation made at the port of entry…

So the Immigration Officer can examine your new invitation letter and let you in. He doesn’t have to if he doesn’t want to, the key words are: “not obliged to consider an application for variation“. You’ll need to show that your meeting was arranged in advance while you were outside of the UK.

That should answer your question.

Having said all of that. These rules are changing in the early part of 2015, and based upon what you wrote you may be affected. In fact, they are considering to combine Business Visitor with General Visitor and have just a single category. The permitted activities under these visas are changing also. They haven’t drawn up or published the transitional provisions yet, so exactly how you will be affected isn’t known. If you are ‘grandfathered’, the above rules will still apply; if not, then you will need to check closer to your actual travel date. Bottom line: skv’s answer is fine.

Adding 18 Feb 2015 update…

This communication from the Home Office…

Thank you for your feedback on the draft visitor Immigration Rules and
Guidance, and for contributing to the workshop discussions. We will be
laying the new Immigration Rules for Visitors before Parliament on 26
February 2015 alongside other routine changes to the Rules and these
will come into effect in April.

We will confirm the commencement date in the next few weeks.

We will be phasing in changes to the IT systems. From April, customers
will not see any difference in the way they apply for a visit visa,
but from late summer they will be issued with new visit visa
endorsements that align with the streamlined visitor routes. We will
make the transitional arrangements clear on our website and in
communications to staff. We would be happy to explain this in more
detail in the lead up to the implementation date.

attending a pre-arranged meeting or interview, a conference or a trade fair (but not selling products or services)

Is what exactly you did the first time and is permitted as per detailed rules here

to attend meetings, conferences and interviews, provided they were
arranged before arrival in the UK and, if the applicant is a board-level
director attending board meetings in the UK, provided they are not
employed by a UK company (although they may be paid a fee for attending
the meeting);

The very reason it felt unlikely to be acceptable to me was because immigration rarely permits someone who is just looking for a job, so my recommendation would be that you make another appointment and then arrive in the UK with an invitation letter, rather than travelling to UK without one.