Once the lump sum is in your account you will be obliged to tell your local authority that you have received it and it may disqualify you from means-tested benefits. You should also tell DWP if you receive any other benefits like ESA or JSA etc. There will also be HMRC to inform if you receive tax credits.
You shouldn''t need to inform them that a sum has been agreed, only when you have received it.
If memory serves if you have savings of £16000 or more then you cannot receive any means tested benefits including housing benefit. According to
this site if you have savings of higher than £6000 (or £10000 if you''re over 60) your entitlement may be reduced.
EDITED to add lower savings threshold information.
Thank you so much LLM. I also thought it would not effect my child and working tax credits if the lump sum is for the deposit for a mortgage.
You''ve relieved me, was panicking as the lump sum is only 30k, and with the tax credits reduced, we would not survive. Kind regards.lena