Celtic and pre-Celtic in Britannia

Is there anybody interested in considering the existence of an IE,
non-Celtic stratum in ancient Britannia?
Starting from the fact that Celtic was a /o/ language, a simple criterion
to separate Celtic and non-Celtic toponyms could be looking for ones that
have an /a/ where /o/ would be expected from Ablaut of a PIE root.

I found:
1) Aballava (Rav.), if this comes from *abel- 'apple'. The second component
could be just the non-Celtic equivalent of Celtic *ab- 'water', instead of
a separated root, often referred as *awe- 'streaming water'. This
conclusion could, in my opinion, be confirmed by the fact that another
relevant toponym in Ab-, namely Abona fl., shows an /o/ in the suffix (so
it should be of Celtic origins), while
2) Alauna, Alaunus fl. (many, Ptol., Rav., Ant.) can be interpreted as well
as 'streaming water', from the root *el-/ol- (in an /a/ language > *al-)
and the *aw- coming from the previous one, in an /a/, thus non-Celtic
language. The same *al- is found in
3) Alobergium (Rav.). Here, -bergium can be related to *bherg^h-, but since
Celtic has already briga 'hill' coming from this root, it has to be the
briga-equivalent in another language different from Celtic. Comapre the
various other descendants of *bherg^h- in all the European domain, and
especially Bergomum (mod. Bergamo), in ancient Gallia Cisalpina, that can
also be pre-Celtic (maybe from the language of the ancient Ligures)
4) Ardaunium (Rav.). Again, a second component *aw-, with a first component
that resembles Skr. ardati 'to flow', Lith. place-name Ardija, but tells
nothing about /a/ or /o/ feature, because of Gk. ardo 'to bedew'
5) Brunavis (Rav.). Here, the same *aw- as a second component, while the
first, if it can be related to *bhru:- 'bridge', cannot be Celtic that
already has briva. Otherwise, if it is from a root (Pokorny) *bhreu-(n-)
'spring', cfr. germ. Brunnen, it tells us nothing about /a/ or /o/ feature.
6) Aesica (Rav.). As many other toponyms in ancient Europe, here the root
should be *eis- and Ablaut-variants, 'rapid' (often said of water). The
version with /a/ couldn't therefore belong to an /o/ language. Apparently
related to the Ablaut-variant *is- are Isca(s) fl. (Ptol., Rav.) and
Isurium (Ptol., Ant., Rav.)
7) Sabrina fl. (Ptol.), Sarna (Rav.). Here I see a descendant (in an /a/
language) of *seu-/sou-/su- 'a juice' > *saw- > *saw-rn-a > Sàbrina,
Sarna > Severn. Compare Savo fl. (Ita), Sava/Saus fl. (Pan), Savia (Tar),
Ohg. sou 'juice', Skr. sava 'id.' But probably on this rather large river a
lot of material has been already written. Somebody can help me here ?
8) Tamarus fl. (Ptol., Rav.) If from *tem- 'to cut', it should be the /o/
Ablaut-variant in an /a/ language. But again we have here also Tamesa fl.
(the Thames) and probably something more authored has been said on it. Who
helps me ?
9) Varar fl. (Ptol.). This has several cognates, both with *var- and with
*ur- (cfr. Skr. vari, alb. urd& 'water'). This root has been explained as
an original *(a)wer- (at least by Villar and, without (a)-, Udolph), who
knows related to *aw(e)- reported above. I found also some "laryngeal"
variant like *uh1r-. However, if *war- is only an Ablaut-variant, it should
belong to an /a/ language.

Will someone comment these considerations?

Antonio