British regulators have been cool to the deal.
Comcast itself had been in talks to buy parts of Fox, so its bid for Sky could be a more direct way to acquire media assets in Europe, analysts say.
"[Disney CEO Bob Iger] has described Sky as the "crown jewel" asset among the Fox operations he is seeking to acquire".
"Sky and Comcast are a ideal fit: we are both leaders in creating and distributing content", Mr Roberts said. Comcast stock was down more tha 5%, Fox was off 2% and Disney fell 3%. The telecommunications giant now heads off against Twenty-First Century Fox Inc.
He said Sky, whose Sky Atlantic channel shows the hit U.S. fantasy drama starring Lena Headey as Cersei Lannister was "an outstanding company" and he was confident regulators would clear the offer.
The cash return plan unveiled on Tuesday would make Persimmon the second-highest yielding housebuilding stock, said Russ Mould, investment director at AJ Bell. They have the resources to fund a much bigger bid.
Sky's company secretary Chris Taylor noted that the company had got an offer from Comcast. Disney could counter with a move for all of Sky too.
Other upgrades include a new, widescreen user created to make its simpler for users to navigate between personalised content (such as "favourited" channels and "most recent recordings") and curated TV and movies.
Fox has since proposed several measures to try to assuage the regulator's fears over the Murdochs' potential influence.
The situation is further complicated by a $52 billion (37.26 billion pounds) deal agreed in December 2017 by Walt Disney Co to buy Fox assets, including its 39 percent Sky stake. "It has great people and a very strong and capable management team", said Comcast Corporation chairman and CEO Brian L Roberts.
But ill-timed scandals about sexual and racial harassment allegations at Fox's U.S. networks and pushback from United Kingdom regulators have plagued the deal.
Not all analysts believe Disney will want to fight for Sky. And if he ups his bid for Sky, the mechanics may get tricky, impacting the price of Disney's own bid for Fox (and with it Sky).
Shares in Sky surged 20 percent to £13.26 in London on the prospect of a bidding war. It foreshadows the predicament that could arise with Hulu, in which the tables are turned - Disney may have majority ownership by way of Fox, and Comcast would be left as a minority stakeholder.