Let me first say I am not expert in Greek or Welsh, let me also say that I am not expert in languages in general.
Having said all that I have made a few observations regarding the Welsh and Greek language and there appears, to me at least, that there is a hint of a connection in their alphabets.
History of the Welsh language.
One thing that hit me when I was researching the history of the Welsh language (links below) was that the earliest record of the Welsh language was around 600AD and that Welsh was written in latin characters.
This seems odd given that the Welsh nation has been in existence long before the Roman Empire and therefore long before latin reached Wales. From this I am speculating that it is impossible for latin to be the original alphabet of the Welsh language.
Wales has had settled farmers from around 4000BC so I think it is fair to say these people were not using the latin alphabet.
So why do I think there could be a connection to the Greek alphabet?
For no other reason than some of the Welsh letters sound exactly the same as Greek letters when used in words and that both languages are around the same age.
For example.
The following Welsh letters can be substituted into Greek words and the sound of the Greek word will not change, the phonetic pronunciation is also exactly the same unless stated otherwise.
ch = χ
dd = δ (phonetic pronunciation of the letter is not the same)
f = β (phonetic pronunciation of the letters differ slightly)
ff = φ (same in latin)
ng = γκ (not a Greek letter but the combination of Greek letters is exactly the same as the Welsh letter)
ll = this is unique to Welsh
p = π (same in latin but phonetic pronunciation is the same in Welsh as in Greek but not in English)
ph = φ
rh = ρ
th = θ (phonetic pronunciation of the letter is not the same)
y = υ
So almost half the letters are the same, I think it warrants further investigation!
History of the Greek Language
The Greek language as it stands today dates to around 730BC which means it does not cover the Welsh language back to 2000 BC
But there is an ancestor of the modern Greek alphabet which extremely close to it and it is called the Phoenician Alphabet.
So while Welsh may not be tied to the modern Greek alphabet I think it is likely that it is tied to the Phoenician alphabet especially given the influence that the Phoenician alphabet has had on latin.
Conclusion
I think it is likely that the Phoenician alphabet was in use in Wales prior to the Roman invasion with the Roman occupation of Wales leading to the Welsh language adopting the latin alphabet instead of the original Phoenician alphabet.
Much like English policy in the later part of the second millennium was to try to eliminate the Welsh language, I see no reason why the Romans would not have done something similar during their occupation of Wales.
Other related links
http://en.wikipedia.org/wiki/Alveolar_lateral_approximant
http://www.cs.ox.ac.uk/people/geraint.jones/rhydychen.org/about.welsh/
http://www.sjsu.edu/faculty/watkins/welsh.htm
http://philenid.0catch.com/Pastor/Greek/L01Greek_History_E2A.htm
Hi, this is very interesting. I would like to delimit Spain around the same time. I believe the history of Western Europe at the time was a bit similar.
There is archaeological evidence of Phoenician and Greek settlements in Southern Spain, as far as the 9th century BC. Iberian inscriptions used the Phoenician alphabet as well. When both groups of people arrived in Southern Spain, they encountered Tartessos, an ancient Iberian civilization whose origin is unknown.
The Greek travelled extensively to create a description places and its people, creating colonies on their way. On the other hand, Phoenicians were experienced sailors and merchants, who would set colonies that would function as ports where to rest, commerce… So it is probable that they did not only get to Spain, but perhaps they managed to arrive to the British isles.
Some links:
https://www.red2000.com/spain/primer/tartessos.html
https://guia-arqueologica.com/phoenicians-and-greeks-spain/