temperatures reached 20.5 c in scotland today , while highs of 17c were seen across the south west and wales .
best of sunshine was in scotland and northumberland , while norfolk , suffolk , essex and kent remained cloudy .
today 's warm weather is the start of week-long spell of sunshine , which could culminate with 21c high on friday .
tourist , in her 20s , had to be rescued in cambridge after toppling into the water while punting with three friends .