'''河口域英語'''（かこういきえいご、'''Estuary English'''）とは、1980年前後からイギリス・ロンドンとその周辺＝テムズ川の（広義の）河口周辺で使われるようになった英語で、イギリス英語の一種。

新中間階層により、そのどちらとも違う新しい英語が作り出されてきた。東京周辺での日本語使用状況と比較すると、大まかに以下の点が指摘できる。

{| class="wikitable"
|+ロンドン周辺の英語と東京周辺の日本語との対照表
|-
!英語!!日本語!!ニュアンス（日本語）
|-
|RP||山の手言葉||それは少々難しゅうございますから…
|-
|コックニー||江戸言葉||おめえさん、こんなこともわからねえのかよ？
|-
|河口域英語||首都圏方言||僕的には十分面白いと思うんだけど…
|}

つまり、

* RP（日本語の山の手言葉にほぼ相当）は上流階級らしさが顕著な言語であり、若干「お高くとまった」印象がある。
* コックニー（日本語の江戸言葉にほぼ相当）はいわゆる下町らしさが漂った言語であり、少々「俗っぽい」印象がある。

これらの言語の話者とはまた違った層の人々が、“自分たちの言語”として作り上げてきたのが河口域英語だといえる。

以前はRPだけで放送を行っていたBBCでも、現在では河口域英語を含む多様な英語の話者を採用しており、また社会の名士とみなされる層の中にも、河口域英語の特徴を取り入れた表現を行う人も少なくない。例えば故ダイアナ元皇太子妃や前首相のトニー・ブレアの英語は河口域英語の特徴が多少あり、ザラ・フィリップス（第一王女であるアン王女の長女）の発音は河口域英語の影響が強い。

コックニー発音との共通点:

'''Estuary English''' is a name given to the formulation(s) of English widely spoken in its estuary, which is where the two regions meet. Estuary English is commonly described as a hybrid of South Eastern Accents, particularly from the construct consists of some (but not all) phonetic features of working-class London speech spreading at various rates ''socially'' into middle-class speech and ''geographically'' into other accents of south-eastern England.<ref>[http://www.phon.ucl.ac.uk/home/wells/przed.pdf A handout] by John C. Wells, one of the first to write a serious description of the would-be variety. Also summarized by him [http://www.phon.ucl.ac.uk/home/estuary/ here].</ref><ref>[http://www.ph-karlsruhe.de/wp/altendorf/research/ Altendorf, Ulrike (2003). ''Estuary English - Levelling at the Interface of RP and South-Eastern British English''. Tübingen: Narr]</ref>

===Features===

Estuary English is characterised by the following features:

* Non-rhoticity. 
* Use of intrusive R.
* A broad A () in words such as ''bath'', ''grass'', ''laugh'', etc.  This is often seen as the litmus test of a South East accent, but it has only spread to rural areas of the South East in the last forty years.
* T-glottalization, i.e., using some glottal stops: that is, ''t'' is sounded as a glottal occlusion instead of being fully pronounced when it occurs before a consonant or at the end of words, as in ''eight'' or ''McCartney'' and it can also occur between vowels, as in Cockney or southern dialects, e.g., ''water'' (pronounced as ).  Females show much higher glottaling scores than males.<ref>[http://www.universalteacher.org.uk/lang/joanna-ryfa-estuary.pdf Estuary English: A Controversial Issue?] by JOANNA RYFA </ref>
* Yod-coalescence, i.e., the use of the affricates  and  instead of the clusters  and  in words like ''dune'' and ''Tuesday''.  Thus, these words sound like ''June'' and ''choose day'', respectively.
*Vowels: 
**  → , , , or :  ''face''
**  → , , , or :  ''goat''
**  → , , , or :  ''price''
**  → , , , or ; the offset may also be centering ():  ''mouth''
** → , , , , or  :  ''trap''
** → , , or  :  ''strut''  
***Realisations of this vowel range widely from a fully back unrounded  and back rounded  to fronted , with predominant central . The back variants  chiefly occur before the velar nasal, as in ''drunk''.  Fronting is most evident in female speech. Male speakers tend to use central to back realisations ().  
** →  in closed syllables; in open syllables it can be  or  :  ''thought'' :  ''core'' 
** → , , or :  ''fleece''
** → , , or :  ''goose''

* L-vocalisation, i.e., the use of , , or  where RP uses  in the final positions or in a final consonant cluster. 
* Use of confrontational question tags.  For example, "We're going later, aren't we?", "I said that, didn't I?"

Despite the similarity between the two dialects, the following characteristics of Cockney pronunciation are generally ''not'' considered to be present in Estuary English <ref name=rosewarne>[http://www.phon.ucl.ac.uk/home/estuary/rosew.htm Rosewarne, David (1984). ''Estuary English''. Times Educational Supplement, 19 (October 1984)]</ref> <ref>[http://www.phon.ucl.ac.uk/home/estuary/transcree.htm Wells, John (1994). ''Transcribing Estuary English - a discussion document''. Speech Hearing and Language: UCL Work in Progress, volume 8, 1994, pages 259-267]</ref> <ref name=alt>[http://www.phon.ucl.ac.uk/home/estuary/altendf.pdf Altendorf, Ulrike (1999). ''Estuary English: is English going Cockney?'' In: Moderna Språk, XCIII, 1, 1-11]</ref>:

* Th-fronting, i.e., replacement of  with  (e.g.  for ''think'')
* H-dropping, i.e., Dropping  in stressed words (e.g.  for ''hat'')
* Double negation.  However, Estuary English may use ''never'' in case where ''not'' would be standard.  For example, "he did not" [in reference to a single occasion] might become "he never did".
* Replacement of  with  is not found in Estuary, and is also very much in decline amongst Cockney speakers.

However, it should be noted that the boundary between Estuary English and Cockney is far from clear-cut <ref> [http://www.phon.ucl.ac.uk/home/estuary/maidment.htm Maidment, J. A. (1994) ''Estuary English: Hybrid or Hype?'' Paper presented at the 4th New Zealand Conference on Language & Society, Lincoln University, Christchurch, New Zealand, August 1994.]</ref>  <ref>[http://www.phon.ucl.ac.uk/home/estuary/haenni1999.pdf Haenni, Rudi (1999). ''The case of Estuary English: supposed evidence and a perceptual approach''. University of Basel dissertation.]</ref>, hence even these features of Cockney might occur occasionally in Estuary English.