Dylan Hartley acknowledged England have "so much to work on", despite making a winning start to their Six Nations title defence against France on Saturday.
Last year's grand slam champions scraped to a 19-16 victory at Twickenham, a late score from Ben Te'o ensuring Eddie Jones' side extended their winning streak to 15 Tests - a new national record.
Although Hartley was understandably pleased with a battling win over a hugely physical French side, England's skipper identified areas for improvement ahead of next weekend's clash with Wales.
"There's plenty to work on," said Hartley in an on-pitch interview after the final whistle. "We got through that one.
"I think a huge amount of credit needs to go to our finishers. Ben Te'o and James Haskell came on and gave us a good bit of go-forward at the end. It was an unbelievable impact from our subs - and big shifts from Maro [Itoje], Courtney [Lawes] and Dan Cole in playing 80 minutes.
"We dug in, we found a way and we'll take something from that. We'll take that win, but there's plenty to work on. It was pretty obvious out there that we need to be a bit more clinical with ball in hand and not so passive in defence.
"There's going to be so much to work on. It keeps us grounded. It keeps us ready for next week [against Wales], basically. We're going to have to be a lot better than that."
England are now just three wins short of New Zealand's record 18-match winning streak for tier-one sides.
An unprecedented second successive Six Nations grand slam would see Jones' men surpass the All Blacks.