I am moving back to university in a few weeks and im looking for a low power tube amp to use while im there. My 20w Marshall DSL is far too loud. Im wondering what amps can deliver American high gain sounds (dual rectifier high gain) at low power. Im currently playing my modded american telecaster with SD hot rails. I just want to know the models so i can try them out. My budget is around £300-350.

Alternatively i would like to connect my guitar to my lap top and play that way. I have a tube powered hi-fi with excellent speakers so that would be another option. I dont know how to connect my guitar to my laptop (vaio) though.

Any help is apprecitated!

for those about to rock . . .
I would look into SS amps for high-gain at low volume, unless you plan on running a distortion pedal into a really tiny tube amp. You might try the Blackstar HT-5 with a boost, but I would still check out SS amps before looking into <20 watt tube amps for metal/hard rock/punk ( whatever it is you would use a Dual Rec for ).

I liked the Hughes & Kettner Edition Blue amps with a boost for that purpose, although they are difficult to find. The new Vypyr amps are worth a look too. I bought one for the exact same reasons you are looking for; wanted super high-gain at university apartment volume levels, and my bigger tube amps just didn't seem like a good idea. Those Vypyrs smoked everything else I tried, and are unreasonably affordable considering how good they sound...plus they record direct to your PC with a USB chord, which was another plus in my book.

The other things you might think about doing are re-amping your DSL if you like the tone you get from that, or an attenuator. There just really aren't that many 5-10 watt tube amps that do high-gain well at low volumes.

Finally, if you've got a tube-driven sound system, you might even consider getting a modern POD, or even a few Sans-Amp pedals, and just running them straight into your system. I've known guys who run PODs into really cold PA systems and were able to get some pretty hot tones, so through a nice tube system it might sound even better.
Blackstar HT-5

2001 Ernie Ball Music Man Axis Super Sport
2001 MIM Standard Strat
Peavey Classic 30 112 Combo.
My Gear
Why even bother buying a little tube amp?

Just go buy a cheap Weber attenuator, there's one for like 65 USD that even has a headphone jack and you can turn off your amp speaker altogether with.

In case you don't know, an attenuator goes between your amp and the speaker and let's you turn the volume going to the speaker way down while still keeping the tone from your amp (hypothetically - but it doesn't sound too bad).

Also, I'm pretty sure the Headphone tap attenuator has a line-out (or just use the headphone out), get a 1/4" to 1/8" converter from some store (do they have Radio Shack in GB?), and just go into the microphone in on your laptop.
If you want to connect your guitar to your hifi then you need a multifx pedal. A Peavey Vypyr with line out would give you that and allow you the option of playing through the amp's speaker. The Vypyr is cheap and they sound pretty good.
Modern high gain tones are mostly based on preamp distortion, so there's no reason whatsoever why a 100W high gain monster like a Boogie wouldn't sound great at apartment volumes.

Stick a good distortion pedal in front of your DSL and you'll get better high gain sounds than you would out of any of the little tube amps on the market (except the HT-5) - they're almost all geared towards vintage 'cranked amp' tones.

I recommend keeping the DSL and using your laptop, as suggested. You'll get massively better sound quality than you will with an amp in a uni dorm. Spend £50 or so on a cheap USB audio interface and if you've got cash to spare, treat yourself to a good pair of speakers or headphones.