There is a lot of rubbish written on this thread I'm afraid and I can't find time to go through each comment to debunk it - though, of course, some are correct.
OP - if this came swiftly after you told them you are pregnant, then bring a case. Maternity dismissal is automatically unfair and there is no two years waiting period.
Go to CAB, or a free representation unit, they will help you prepare an ET1 online (or, just do the ET1, they are not hard) and send the tribunal claim form. Chances are, they will settle anyway (ACAS will step in and negotiate for you).
www.gov.uk/government/publications/make-a-claim-to-an-employment-tribunal-form-et1
They have to prove they did NOT do it for this reason, you do not have to prove they DID.
Also - there is a statutory right to employment particulars after 8 weeks and it sounds as if you have not got that. This claim cannot be brought on its own to a tribunal but can be brought in what is known as a 'piggy back claim', so when you put the maternity dismissal claim in, add that - it's a statutory award and as it's a matter of fact there is nothing to prove, you don't have it, they can't show you do (because you don't) so if nothing else you will get that awarded. This is between two and four weeks pay.
uk.practicallaw.thomsonreuters.com/4-200-2038?transitionType=Default&contextData=(sc.Default)&firstPage=true&comp=pluk&bhcp=1
re notice - you are entitled to one week paid notice and pay for accrued unused holiday entitlement.
I would say sales is brutal but this is too soon for pipeline to come through plus the fact it's when you've told them you are pregnant - it's clearly unfair dismissal (without the time bar).