As I said before all my tests have been with BT. I am stuck with this shite ISP unfortunately...
Traceroutes from 2 x different BT ADSL lines:
Tracing route to ukbouldering.com [209.135.140.14]
over a maximum of 30 hops:
1 1 ms <1 ms <1 ms
www.routerlogin.com [192.168.0.1]
2 32 ms 31 ms 31 ms host81-148-0-1.in-addr.btopenworld.com [81.148.0.1]
3 31 ms 32 ms 32 ms 213.120.178.141
4 32 ms 31 ms 31 ms 213.120.177.98
5 32 ms 31 ms 33 ms 213.120.176.22
6 * 31 ms * 213.120.176.178
7 32 ms 32 ms 34 ms 213.120.176.121
8 32 ms 32 ms 31 ms core2-gig14-0-0.faraday.ukcore.bt.net [62.172.102.153]
9 33 ms 32 ms 33 ms 62.172.103.45
10 32 ms 32 ms 33 ms transit1-xe0-1-0.ealing.ukcore.bt.net [194.72.9.234]
11 32 ms 32 ms 32 ms t2c1-ge11-0-0.uk-eal.eu.bt.net [166.49.168.29]
12 33 ms 33 ms 34 ms t2c2-p3-1.uk-lon1.eu.bt.net [166.49.208.110]
13 33 ms 33 ms 33 ms t2a1-ge7-0-0.uk-lon1.eu.bt.net [166.49.135.110]
14 48 ms 245 ms 228 ms gi8-44.mpd01.lon01.atlas.cogentco.com [130.117.14.49]
15 34 ms 34 ms 33 ms te1-8.ccr01.lon01.atlas.cogentco.com [130.117.3.226]
16 52 ms 51 ms 51 ms te0-0-0-0.ccr21.ams03.atlas.cogentco.com [130.117.1.109]
17 51 ms 50 ms 51 ms te3-8.ccr02.ams03.atlas.cogentco.com [130.117.0.33]
18 120 ms 119 ms 120 ms te4-2.ccr02.ymq02.atlas.cogentco.com [154.54.0.74]
19 149 ms 149 ms 149 ms te8-7.ccr02.ord01.atlas.cogentco.com [154.54.28.5]
20 144 ms 145 ms 144 ms te4-2.ccr01.stl03.atlas.cogentco.com [154.54.27.30]
21 144 ms 143 ms 143 ms river-city-internet-group.demarc.cogentco.com [38.104.162.10]
22 142 ms 142 ms 143 ms 205.242.181.29
23 168 ms 141 ms 141 ms r-1.core04.stl.rosehosting.com [206.196.99.250]
24 142 ms 142 ms 141 ms vs314.rosehosting.com [209.135.140.14]
Trace complete.
Tracing route to ukbouldering.com [209.135.140.14]
over a maximum of 30 hops:
1 3 ms 1 ms 2 ms home [10.0.0.1]
2 34 ms 34 ms 34 ms host81-134-96-1.in-addr.btopenworld.com [81.134.96.1]
3 33 ms 32 ms 32 ms 213.120.182.141
4 33 ms 34 ms 32 ms 213.120.161.82
5 34 ms 34 ms 32 ms 217.41.222.30
6 33 ms 32 ms 33 ms 217.41.222.178
7 33 ms 34 ms 34 ms 217.41.222.121
8 33 ms 243 ms 32 ms core2-gig4-0-0.birmingham.ukcore.bt.net [217.32.170.73]
9 261 ms 42 ms 248 ms 62.172.103.86
10 54 ms 39 ms 36 ms transit1-xe1-1-0.ealing.ukcore.bt.net [62.6.200.138]
11 39 ms * 40 ms t2c1-ge14-0-0.uk-eal.eu.bt.net [166.49.168.25]
12 45 ms 38 ms 38 ms t2c2-p3-2.uk-lon1.eu.bt.net [166.49.164.138]
13 39 ms 38 ms 38 ms t2a1-ge7-0-0.uk-lon1.eu.bt.net [166.49.135.110]
14 41 ms * * gi8-44.mpd01.lon01.atlas.cogentco.com [130.117.14.49]
15 40 ms 42 ms 38 ms te3-1.mpd02.lon01.atlas.cogentco.com [130.117.2.26]
16 49 ms 48 ms 48 ms te0-3-0-0.mpd21.ams03.atlas.cogentco.com [130.117.2.82]
17 49 ms 50 ms 50 ms te1-8.ccr02.ams03.atlas.cogentco.com [130.117.49.206]
18 * * * Request timed out.
19 * * * Request timed out.
20 * * * Request timed out.
21 * * * Request timed out.
22 153 ms * * static-216.87.62.241.primary.net [216.87.62.241]
23 * * * Request timed out.
24 * * * Request timed out.
25 * * * Request timed out.
26 * * * Request timed out.
27 * * * Request timed out.
28 * * * Request timed out.
29 * * * Request timed out.
30 * * * Request timed out.
Trace complete.
Not sure if this helps, but could be a routing issue somewhere?