Hi.
Yes you need an ECA for any education/degree done outside Canada, for which you are claiming points.
Immigration will usually require an assessment for only your highest degree, as it will give you most points, which in your case is Postgraduate from England. Of course, if you choose to, you can assess both degrees, as you'll be paying the same price anyway. It only depends on how easily you can get grade sheets from your school in Bangladesh
.
There are multiple ECA organisms to choose from depending on what kind of degree.
But usually, people will go either with WES or IQAS.Check this link:
http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=681&top=29
Then explore the website to see exactly which documents are required for the degree you want to have assessed.
If you are interested in applying for immigration to Canada,
assuming you fulfill all immigration program requirements, ECA and Language Tests (IELTS and/or TEF) should be done as early as possible as they will require the most amount of time.
Expect at least 40 days for the whole ECA process, and 30-40 days for language test processes, from registration to results.
However, from what I understand, you just graduated... And one of the most important criteria is a minimum of 1 year of continuous full-time work experience.
Do you have that?
Cheers;